MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - 1275 cc poor running

Hello,

I have a 1974 mark 3 midget. The car is running and drivable, but is running very rough.

The idle speed seems a bit erratic. When i get to approximately 3500 revs, if i accelerate slowly the exhaust sound is funny and i often get back fires. If i accelerate hard the problem goes away. Often get back fire when deccelerate.

I think this may be a tunning issue. Dont really know where to start. Have twin su carbs.

Any advice, and or the address of a good tuner in the brighton area would be gratefully recieved.

Many thanks.
christian wilson

The obvious question someone is going to ask is whether it ran ok previously and just "developed" this problem.

I think the first thing I would check is the distributor. Are the weights and vacuum doing their job?
Graeme W

Christain,

Back fire or popping as there is a difference. Back fire is unburnt fuel whereas popping results from a lean mixture and is often evident on the overrun when you decelerate so it sounds like a fueling issue.
David Billington

Id think a leaky intake, or dissy timming related, check your points

But .. id say a good clean up of the carbs and retighten everything from the carbs to the head and then give a good look over the ignition system... Heck id even check valve clearance as weelll
Prop and the Blackhole Midget

Hi Christian,
a copy of the Driver's Handbook that would have originally come with the car new will help you with this matter and lots of other ownership matters

if you've not already got a copy a reprint is only 8 and best investment you'll make in the car - (Ref: 0053) - http://www.mgocshop.co.uk/catalog/Online_Catalogue_Handbooks_5.html
Nigel Atkins

Many Thanks,

Graeme,

Was working fine but has slowly developed this problem. Have got a new set of poimts and condensor. Going to clean and fit. Not sure how to check weights?

David,

More of a pop than full blown backfire. Fitted a moss electronic fuel pump. Not sure if this could be problem, or carb settings. Not sure how can check?

Prop,

Will static set distrib. Haynes says 7 BTDC. so will give it a go.

Thanks for all your help....fingers crossed...let you know how it goes.
christian wilson

Christian: if you look in Haynes it tells you how to access the weights. Really all you can do is check the weights and springs are still there and attached and that the base plate can move with the weights. Also check that the vacuum pipework is connected both ends.

If you use a strobe on the ignition you should see the advance working as you rev the engine.

It might not be anything to do with this but it is easy enough to check. It just seems to me that if you are having trouble at higher revs and different throttle openings then not getting the correct advance from the dizzy might be a cause.
Graeme W

If it ran well before leave the timing alone - it rarely changes on its own !

Only change replace one thing at a time !

Sounds like it needs a good service.

Check / replace points - gap setting is vital.

Clean carbs as manual i.e. dashpots/free to drop etc - carbs should not go out of adjustment easily on their own.

R.
richard boobier

Just to let you know....

The points on the car were in a terrible state. The replacement i got were the wrong ones so i put an electonic accuspark module in. I had been toying with the idea of swapping over to this for a while.

Checked springs and weights. Seemed good.

Car running much better. Just need to check carbs and timing as idle revs still seems high.

Have found the TDC mark on flywheel. For future reference what is the best way to turn the engine to set valves?

Many thanks for all the help and comments. Much appreciated. Great forum.
christian wilson

>>Have got a new set of poimts and condensor<<
many modern condensers are poorly made and so are some modern CB points

I'd try checking the new points gap, you need to check and reset as required at a few weeks of 500 miles but some don't last that long before closing up

if it's not that then put the old condenser back in

check plugs of course and dissy cap and rotor and HT leads

(could be also perhaps muck in fuel system somewhere)

for timing you really need to follow the order of - tappets, points, plugs, timing, (carb) mixture

I wouldn't get into dissy weights yet but oiling and lubing the dissy is a good idea (info in the Driver's Handbook I know you have a Haynes but the Driver's Handbook is often better and without the errors in Haynes)

personally as soon as you can afford I'd suggest getting rid of those horrible CB points and worn dissy, I like the 123 dissy as it gives the car a great improvement - available from Peter Burgess

in the meantime for good quality condensers, CB points rotors, dissy rebuilds I'd suggest the Distributor Doctor - http://www.distributordoctor.com/

as has already been said a full and proper service will sort out many problems and prevent more - Driver's Handbook for prevention, Haynes for repair

also regularly driving the car will help you and the car and an occasional blow run or long journey will also help

don't worry too much about getting setting figures exact on these cars as they're not factory fresh now but if you need any setting spec they're in the Driver's Handbook (a hint as to what to buy)

good luck
Nigel Atkins

Christian,

You will need to reset the ignition timing, the Acuspark units can alter your timing buy as much as 10 deg. As for seting the valve clearences, I remove the plugs, put her in 1st gear and rock the car forwards.
P Ottewell

You may have already discovered this but I found you can't set electronic ignition statically with a light across the "points". You need to use a strobe.
The other useful thing to do is to make up a small sheet metal bracket which sits above the timing pulley and onto which you can transfer the timing marks. Pick up a timing cover bolt to locate it. It is much easier to work with than the timing marks underneath and hidden by the crossmember. Just watch the fan doesn't collect the strobe or your fingers.


With regard to your running problems, it's worth checking both carb pistons are free to lift and drop and that the correct oil is in the damper chamber. Haynes suggests engine oil but I have also seen recomendations for "3 in 1" viscosity oil.
Graeme W

Yes - I had similar issues solved by adjusting tappets, changing out the plugs - may as well as they are not expensive - and having electronic ignition. I set that by simply rotating the distributor body until I obtained the best revs - as you do with points....Agree that carbs should not go out that quick, but personally I would clean out the main jets and ensure there are no leaks anywhere - especially a the manifold/vac advance.
Mark O

sorry Christian I didn't see your post just before mine (I was probably still typing mine)

also have look at the YouTube (John Twist) University Motors Ltd videos for setting the tappets and carbs, there are more than one video on each in the 200+

also one about being careful not to snag those delicate wire on the ignition heads
Nigel Atkins

Dont use "static" timing,

the purpose of static timming is to just get the engine running after a rebuild or dissy replacment

You want dynamic dissy timming....and with the new ignition system, you do have to retime the dissy, if its to advanced you can do some serious damage

The easiest way to turn the engine is to stick the car in 4th or 5th and grab the front bumper and pull the car... Its easy to do

Or... On the selinoid pull the red / white wire and replace with a 1 foot long jumper wire and brush the other end agianst the pos batt post ..make sure the key is in the on position and the coil disconnected and the car in nutreaul
Prop and the Blackhole Midget

Graeme, as you've found the lamp doesn't work but there is another way. Take the main HT lead out of the dizzy and locate it close to an earth (cyl head nut works) and rotate the dizzy until you get a spark. Just to make sure rotate it back a few degrees and as you slowly rotate the dizzy body clockwise you will get a spark at the point the electronics trigger.
Prop, agree this is to get it started and dynamic is the way to go thereafter.

Christian, turn the engine with a spanner on either the crankshaft or the alternator/dynamo pulley. You'll need to apply a bit of pressure to the belt to ensure the engine spins if using the alternator/dynamo. Obviously this is with the plugs removed...
Best of....
MGmike
M McAndrew

I have a strobe lamp that does the job although it probably older than my sprite now. Just need to be careful down amongst the fan blades! But at least I can check it at vario0us engine revs, which is useful.

In the 60's I had a Mk1 and then various minis, spitfire and so on. Gradually as cars were replaced with more modern versions a lot of these bits fell into disuse and got lost with various housemoves. Since I bought the Sprite 18 months ago I have had to have a good search round to find them again! The one thing I didn't fancy using was a 40 year old Easibleed! I could just imagine old brittle plastic going bang under 20psi air pressure.
Graeme W

Thanks so much for all your advice.

Have a strobe light so will have a go at setting this at the weekend.

Will also clean up carbs. Sometimes it idles at 1500, sometimes at 1000. Not sure if this could be a sticky carb, or choke.

Will rebuild, clean and reset carbs.

Fingers crossed, that will do the job.

Yes, the idea of using the strobe light whilst looking under the car seems a tad daunting!!!

Many thanks.
christian wilson

It really is worthwhile transferring the timing marks to a new bracket above the pulley rather than using the factory marks below. It took about half and hour and makes setting timing so much easier. Just watch out for the fan though! Otherwose you may have no fingers to cross (ouch!).
Graeme W

X2 Graeme

It really is daunting, what i found was to jack the car up about 1 foot get on your back with your head at the front of the car and you can just see the timming marks.... I only did it once, and wouldnt want to do it again

Everyone should try it at least once... Cause it really is a disney E. Ticket ride to have the engine running and your right in the path if the tranny decides to shift into gear by its self...its a real comming to jesus moment,.... hahahaha

Enjoy the E. Ride

Prop
Prop and the Blackhole Midget

Prop: I don't know why they put them underneath. It's not as though you can look straight at them because the cross bar frame section is in the way. And if you want to adjust the timing you have to get back up into the engine bay again so the idea of being accesible from a car lift doesn't seem to make sense either.
Graeme W

Graeme,

When you talk about a new timing bracket...do you mean simply copy the pattern of the pointers on the factory one and then bolt it so it sits above the pulley? Where do you fix the bracket?

The idea of being able to turn the distributor and see the change on the timing marks with the strobe does seem rather appealing!!!

Prop: call me a whimp..but anything for an easy life my friend. Hahaha.
christian wilson

I'll see if I can take a picture of my crafted bracket(!) if it hasn't fallen off.
Graeme W

"idle erratic" and "backfires" are both clues to worn butterfly shaft/ bushes on an SU. One can sort of tune to improve things to some extent but the erratic idle will persist.

Try smearing some Vasaline around the boss that the throttle shaft goes through to see if this temporarily improves things.

If there is wear, often it is sufficient to just replace the butterfly shaft as this wears sacrificially rather than the bushes. But in a bad state, the throttle body will need rebushing and reaming to match a new shaft.
Guy W

Graeme,

much appreciated.

Guy,

I have an SU rebuild kit. The kit comes with new butterflies, shafts and what appears to be bushes. Whats the best way to remove the oldens? Is it easy?

Many thanks.
christian wilson

Christian,

Basically what you do is set the crank shaft pully mark on the timinng mark, then you make a new mark on the crank shaft oully at the top and then you mount a pointer that points to the new mark... You can also get degree tape from speed and hot rod shops that can be applied to the crank shaft pully that works with the new pointer

Also axle grease works on the butter flys shaft ends also, but id also look at he intake manifold... Which i mentioned way early on...your looking for vacume leaks

Prop
Prop and the Blackhole Midget

Christian,

Undo two small black screws that hold the butterfly disc to the shaft. The ends of these screws are split and splayed to stop them coming loose and being swallowed by your engine (not good!). Once removed the shaft will then just dismantle.

Chances are that you don't need the bushes. If you do, then the job becomes considerably more complicated as they need aligning and reaming after replacement. Although there are "dodges" to assist (Google ChicagolandMG Club and look at their technical articles)

When reassembling the butterfly disc make sure to put it in the right way round as the edge is chamfered to match the carb venturi - check and if necessary mark it before you dismantle. Ideally replace the two little screws with new. Certainly splay the ends again and use some locktight on them too.

Before all this do the test I suggested with vaseline to check that is actually at fault. I may be wrong with my "diagnosis at a distance"! Or spray WD40 onto the spindle bushes whilst it is running and listen for a change in engine speed. Also check and feel for sideways slack in the butterfly shaft where it goes through the bushes - there should be none, or virtually none.

Prop,
you are right, it could be any vacuum leak as you said earlier. The reason why I thought specifically of the butterfly shafts as that if worn these make getting a consistent tickover especially difficult. Seemed like an extra clue to me!
Guy W

Great catch guy...

To be honest, i hadnt thought of the carb spindles... So im a bit jealous of you, my vanity has been spoiled,

no NOT my virginity, thats still fully intact and gaurded from corruption....hahaha

Vanity, vanity is my favorite sin

Prop
Prop and the Blackhole Midget

Change them for a single HIF44!
Lawrence Slater

Lawerance.... "Change them for a single HIF44!"

Efficiant yes, easy yes, decent power curve sure why not

but Doc holiday, jessy james, and billy the kid, always pulled 2 from there holsters...1 will make you a hero, but 2 makes you a legand

Prop
Prop and the Blackhole Midget

Now that's clever Prop. Linking su's to the old west. lol.

How come you didn't get Clint Eastwood and JW in there too? :)
Lawrence Slater

I love john wayne and clint eastwood...But they are just pretenders to the thrown

ive always loved and immulated the real gun slingers as a kid...esp jessie james due to my close proximantie to his escaldes

Hard to belive serial killers were every young boys heros back in the 70s...but we do love the guns

I think it was there individuality and rebellion agianst high corruopt socity and the law that was so appealing and still is today

Prop
Prop and the Blackhole Midget

Hi,

Just a little update.

Checked timimg with strobe, have reset but wasnt actually too far out.

Carbs are off. Have stripped them down and cleaned them. They were very dirty and a bit sticky. The butter fly shafts do seem quite worn so will replace. Just off to start the rebuild of carbs. Will refit and tune tomorrow. Hopefully can get it running well. Will tighten down the manifold and replace gaskets so hopefully wont have any leaks.

Prop,

Did the timing under the front end...still alive to tell tale, but quite a faff. Will put a new mark on when get a chance. As far as the wild west references go all i can say is "go ahead prop, make my day" hahaha.

Many thanks for all your comments and advice. Hopefully this thread will now dissapear into the archives and my mg will be purring like a kitten.
christian wilson

Congratz on maintaing life,

wasnt that just fun....after that exercise i wanted to go all in and play " how close can i get my neck tie to the spinning fan at 4500 rpms....did you feel the same impulse, hahahaha

Just so you know... There is an actual timming mark at the edge of the pully, and its NOT the dimple....."i did it also"

Keep us updated, and hang around, its a fun group

And thanks for playing... "Am i really going to stick my head up my butt backwards to check the timming"....what a wonderful game of human vs running car roulette

Prop
Prop and the Blackhole Midget

I think i spoke to soon.

Replaced carbs and gaskets. Hooked it all up and gave it a tune. Seemed to be running fine. Took it for a run. Got a few miles down the road and then i started to loose acceleration. Coasted to a garage on tick over. Then when accelerated engine cut out and would not start again.

Got a tow back home. It was turning over but not firing. Fiddled with dissy and got it to start but revs were jumping up and down like a yoyo. Then just cut out.

Is my advance on dissy knackered? does this sound feasible? I have now given up in disgust. Think it may be a new dissy. Should I just get a replacement, or go for a different one? Its a lucas 25d4.

Once again thanks for your help in advance...no pun intented!!! hahaha.
christian wilson

I still belive this is carb / fuel related....it ran fine until you ran it to E. On the gas guage and filled at a gas station of unknown quality

And thats when it all started....

But you just said no spark this last time...how sure are you there was no spark...hard to see at mid day in bright sun


If its true there is no spark, i wouldnt be so fast to blame the dissy...id check the coil to see if it is super hot....if it is, you got a double grounding issue, a new screw from the fire wall into the wiring harness or an old wire chaffing on a sharp metal edge of the car body

If not then start back tracking it...aka, why is there no spark at #1 spark plug, is there spark at the 3 remaining spark plugs, if not, pull the coil wire from the dissy and check to see if there is a spark from the coil wire, if there is a spark then the issue is in the dissy, the cap is cracked, the carbon rod is damaged, the grond wire in the dissy is bad, you got a black rotor bug instead of the red rotor bug, (very common mistake) or an issue with the points and condenser

But unless the points plate or shaft is trash keep the dissy as its already curved to your engine...a new dissy means it will need to be recurved unless you do a 123 tune from peter burguss, but that wont solve an issue outside of the dissy, infact if the issue is outside the dissy then it could release the hidden blue smoke inside your NEW electronic dissy, and once the blue smoke exits, its hard to buy new smoke and reinstall it

Prop
Prop and the Blackhole Midget

it might not be your dissy as such

it could be:
the Accuspark or it's delicate wiring
CB points worn, dirty or closed up
a new condenser faulty if you've fitted a new one
coil
rotor arm (poor quality if new)
dissy cap
king lead
poor battery or earth connection
poor electric connection somewhere
LT side
fuel side
petrol cap not venting

plus more

for tuning it's this order, tappets, points, plugs, mixture

John Twist (200+) videos can help -
http://www.youtube.com/user/Universitymotorsltd

as can the Driver's Handbook

and Paul's site, it's for MGB but most things apply to Midget too - http://www.mgb-stuff.org.uk/hometext.htm

IF you have to change the whole dissy then look at Distributor Doctor and for rotor arms, condenser, points ect - http://www.distributordoctor.com/

or better still have a fully electronic dissy and not just the head, it'll improve the starting, running and performance of the car - http://www.mgcars.org.uk/peterburgess/123.html

if your car is serviced then setting it up with the 123 installation on the rolling road will be the icing on the cake, great value, low priced - http://www.peter-burgess.com/page28.html
Nigel Atkins

But before i did anything...id make certian there is spark or no spark at the plug wire...put you finger on the spark plug bare lead and spin the engine... Only true easist way of knowing for fact...if there is a spark the only real long term damage will be the desire to buy a double wide and put the fridge on the front step...its a red neck thing... But the feeling will pass in a few weeks
Prop and the Blackhole Midget

I was typing my post as Prop posted his previous post but I think it still stands and the links are worth following and keeping anyway
Nigel Atkins

Nigel... Great call on the gas cap, that is a real possiability, esp if he filled the tank up full and very little air in the tank

When the engine finally dies...remove the gas cap and lusten for a swosh suction release sound, if it does, the gas cap vent is clogged... It will run fine untill the air inside the tank is sucked out the fuel pump ..
Prop and the Blackhole Midget

Looks like nigel and i are sleeping in the same bed on this one...thank god its not at the same time....lol

Double :o

Prop
Prop and the Blackhole Midget

am I in your nightmare or you in mine?

petrol cap is one I've learnt (or relearnt, can't remember) from this BBS

as usual more detailed information of what has happened when and what been done when with logical diagnostics being applied would be better with more questions and answers
Nigel Atkins

Also check the rubbing block in the dissy for rust and pitting

the part that the points arm rides on....if its rusty or pitted badly it can act like sand paper , wiping of the lube quickly and then wear down the rotor arm thus closing the points...you did say the rotor arm was worn down badly on the set you replaced...alittle emery cloth will re-shine the rubbing block very nicely... And asome wd40 will help as a cutting oil for the emery cloth


Prop
Prop and the Blackhole Midget

can't let it go - lubing and oiling the dissy is detailed in the Driver's Handbook :)
Nigel Atkins

nigel,

We may not even exist... We could be the playful sheep in the imagination of Arie.

Now thats a triple :o with a side of :$

Prop
Prop and the Blackhole Midget

If the fault is electrical then two quick things to check:
a) does teh tachometer needle go into spasms when the misfire starts?
b) open the bonnet with the engine running in the dark and look for erratic sparks jumping around plugs, leads, dizzy cap etc. The darker the better for this, so all lights out. Just don't do it parked on a busy highway with all your lights out!
If you spot some blue tracery then you need to identify it in the dark so the technique is then to hold onto the cable/ whatever to check what it is. Finding it will give you a real buzz, or at least a satisfying tingling sensation!
Guy W

Don't stick your finger up the plug lead if you have a pacemaker or are of nervous disposition! I'm sure it can be checked out without such a self sacrifice. It can really hurt - not the shock but clouting your head on the open bonnet when you leap 6' in the air!

It couldn't be water in the fuel could it? There was recently another post here about that and some of the symptons sounded similar. Something I have no experience of.
Graeme W

if you've got the bonnet up looking for a light display and it's not a damp night you could spray a mists of water to help light things up rather than making a grab or a shock
Nigel Atkins

Nigel

Id call that a ""BUZZ"" Killer....hahaha
Prop and the Blackhole Midget

Prop,
you could also spray your hands, head and hair if you want a bigger buzz

I once had a HT lead that sparked out and I could see it even parked under a street light
Nigel Atkins

Kidding aside, anytime you can test for a spark by.other means, im going for that, luckly i think ive gone for the red neck hill billy spark test maybe less then 5 times over a life time...heck they do make tools for that....hahaha

But the dark garage works well

Prop
Prop and the Blackhole Midget

Wow, thanks for the the comments.

Its nice and dark and ive got my rubber boots on. I tried turning the engine over...no blue sparks, flashes, nada. I took out number one plug held it to the block..cranked the engine no spark. Went to number 3 plug no joy.

Popped off the dissy cap...wiped the little magnetic accuspark donut clean. wiggled the base plate about, checked it could move. No points, no condensor. Tried it again. It started up. Twas cold so choke on. Idles o.k.

Then put down the accelerator and held it still part way down. Revs went up to around 4000. Then revs went beserk. Started going up and down like a yoyo, as if i was pumping the accelerator, even though i was holding the pedal still. Going from 1000 to 4000.

Any ideas? Distributor?

Nigel,

I have purchased the owners book. Thanks, great tip. Have also enquired regarding a replacement dissy.

Prop,

call me faint hearted, but didnt fancy putting my tounge on the spark plug lead!! I am sure the price of a new dissy will be shock enough.

Another question...when you rev an su carb...does the needle and piston go right up the air chamber? (ie, dissapear up past the top of the hole on the carb)

Many thanks.

christian wilson

Daft question but you do have oil in the dashpots on the carbs?
Graeme W

Hi graham,

Not daft at all, you are dealing with a complete newby when it comes to Su carbs. When i cleaned the carbs out, refilled with new penrite su damper oil. So should be good. Filled the hollow piston rod to just below the top. Put the damper back in.

The carb pistons lift freely using the piston lifting pins and drops back down to the bridge. However, on one carb if i lift the piston right up to the the top of the hole in the carb it is a bit slower to return than the other. Does the piston go this far when driving the car, of does it move just as far as the lifting pin goes?

Many thanks.

christian wilson

Christian, when in use and the throttle is open wide the piston will go pretty much right in to the dashpot chamber, which as you've found out is well above the lift of the pin. If the piston is slow to return try it without the damper to see if this is holding it up. If still the same remove the dashpot again and give it a good clean and check the springs are the same in each of the carbs. Do you know if the carb's the closed circuit type or do the dampers have a little bleed hole in the top?

M McAndrew

Christian,
when you get the Handbook email me and I'll send you the list of the very few updates I've found for it

as regards carbs you could also check damper spring type, if it's stretched and which way round it's in along with needles secure and not bent - for all this see the John Twist videos on matching dashpots, plus there are two explaining SUs and two about tuning the carbs

also see his video about those delicate wires on igniter heads, they can be scuffed or nicked inside the dissy if too tight or too loosely secured and they might get damaged outside the dissy
Nigel Atkins

Surging can be a number of things

But id get your ignition sorted 1st ... It would seem you have a short in the dissy somewhere.... You said you giggled the wires in the dissy and it fired up.....fix this 1st

Surging can be a vac leak, fast idle speed set to high and timed retarded to compensate, low coolent level, the beginningss of a bad head gasket, and issues with ignition system aka weak springs, and leaky vac advances. Ect....but agian, these can wait, till after the ingition is sorted or you will be chasing your tail
Prop and the Blackhole Midget

Hi all,

thanks once again.

M Mc Andrew,

The damper cap has a small hole in it. Cleaned the offending carb. Re-fitted and now seems to be dropping fine. I trust that it is now sorted. I hope i didnt just have my finger over the little hole!!!

Nigel,

will have a look at the john twist videos when finish this. Thanks a lot.

Prop,

In true red neck style you are right. Need to sort the problem with dissy first. Shall make this top priority. Unfortunately, it so damp, dark, and misserable here at the mo...have to wait till weekend before i can have a go. Ahhhh what i would give for that bright big american sky!!!

christian wilson

Christian,
looking at some of those videos and reading the book now might help you with your current problems

do you know which problems still remain

seems a bit too erratic for as perhaps you could add in vacuum or manifold problems or leaks
Nigel Atkins

Hi Nigel,

Videos were great. Really useful and have helped a lot.

The problems seem to be as follows;

1) electical problem with dissy...means engine turns over but doesnt catch. Fiddling with dissy cap off lead to engine firing and starting.

2) when engine runs goesa fine on tick over. When press accelerator revs pick up but then fluctuates wildly and cuts out.

At weekend will have a good look at distributor and see what I can do to sort this. If get lucky with disy will look at carbs and tuning.

Yeah, the fluctuating revs could well be a leak when under pressure (high revs). I did replace the gaskets on the manifold to carbs...but not the gasket on manifold to head. I just tightened up the bolts. Will have a look and see if it has blown anywhere.

In short...lets hope its a nice weekend as the car is outside. Fingers and toes crossed.

Thanks for your patience and advice.



christian wilson

When i was a kid, i had an old couger that did similar... Tore my heair out... It ran great and 5-10 min later...it ran like crap andd backfired alot and died and wouldnt restart for several hours

It had a hair line crack in the dissy cap. Along one of the spark plug post, when cold it ran fine but once it heated up to temp....it was an issue

Did you check to see if you got the black or red, rotor bug, the black ones have got problems....you want the red ones

Prop
Prop and the Blackhole Midget

Problem with long threads is a danger that the plot gets lost, so apologising if this is repeating but......

I think I would replace distributor cap, rotor arm and leads unless your's are known to be ok. THere are lots of associated problems and it would be worthwhile eliminating them for certain, particularly as you do seem to have positive symptoms in this area.
If your car is outside them susceptibility to damp around the dizzy could be a problem made worse by dubious condition of that bit of kit.
Graeme W

Before spending ANY more money, I would do the following.

1). Put the points back in, set at 15thou, and set timing to static.

2). Turn up choke jets on su's, and turn back down 11 flats each.

3). Make sure your fuel bowls are full of fuel and not sediment. Is the fuel flow consistent?

Get it going from this, and then make changes. Your dealing with too many unknowns at the moment.

You earlier comment was, "Was working fine but has slowly developed this problem."

Go back to this point in time, and look for THAT problem.

If you can limp it to me, I'll take a look if you like.

Lawrence Slater

without going into the usual arguments of why I always suggest doing a staggered 36k-mile service/check up asap on a car new to you I think at this point I agree with going back to known functioning parts as Lawrence has put
Nigel Atkins

whaa thankee kinly fer agreen with me Naagel. :)
Lawrence Slater

Hmmm ... Is that the sound of dueling bangos,

Prop
Prop and the Blackhole Midget

Lawrence

Seem to remember some similar comments in the early posts.

R.
richard boobier

I agree with Lawrence saying similar to Richard

and agree with Richard mentioning a good service - que my multi-worded initial advice . . .

no I wont

I think L's got Prop's keyboard
Nigel Atkins

Round
Like a circle in a spiral
Like a wheel within a wheel
Never ending or beginning
On an ever spinning reel

That's how these threads go, lol.
Lawrence Slater

Oh those were the days !!!

No not another song LOL.

L we must be of a similar generation ?


R.
richard boobier

. . . my friend, we thought they'd never end

but I'm (just) too young to know that circles song
Nigel Atkins

We maybe richard, esp if you prefer the original thomas crown affair to the remake.

But these days I prefer Anthony, to Mary, in the Hopkins stakes Nigel. lol.
Lawrence Slater

"Like a circle in a spiral
Like a wheel within a wheel
Never ending or beginning
On an ever spinning reel"

Thought you were describing how a diferential works
Guy W

I've no idea which, who, Anthony is (Tony Bennett?)

I always think of a bloke singing the circles song and had no idea Sting has covered it

I wonder how Christan is getting along
Nigel Atkins

Lecter Nigel. He of canibalistic tastes.

It does sound like a diff at that Guy. Bet the composer didn't think of that.

PS Nigel, and Dusty.
Lawrence Slater

I guess it is what a cannibal might sing to himself when lost in thick mist on a Welsh mountain.
Guy W

Hi all,

Am fine...but had a load of computer problems.

Haven't attempted anything as too dark and dreary here.

Will put points back on if cant see an obvious probs with dissy.

Let u know how get on at weekend.

Cheers.
christian wilson

keep us posted Christian

sorry L I was confusing the two songs and missed the surname connection

I did look up the singer as I've heard the Dusty version before but it's not the one I remember - Noel Harrison was the male singer that had a big hit with it and it seems whilst Dusty's is well remembered it wasn't a big hit at the time as such

Anthony Hopkins got me think about the more Hollywood remake of the superior early film called Manhunter with Brian Cox as Lektor but the more Hollywood version did have Jodie Foster in it and I do find her very easy on the eye
Nigel Atkins

Yup christian, do let us know, and meanwhile we'll continue to digress. lol.

I agree the Manhunter film was very good, and if the remake hadn't come along, it would be a classic - actually it is still very watchable. But hopkin's Lecter, and the subsequent films have trounced Manhunter imo.

This is one of the few series, I find satisfying in both the book and film versions. I find, to my surprise, that I even like both versions of the end of "Hannibal". In the film he leaves Clarice behind, whereas, in the book, they run off together.

I'm waiting for what I hope will be the final instalment, before Hopkins dies or gets too old to play Lecter again. I wouldn't be so happy to see the film run on and on and on, with another central actor. I think Jodie Foster was the better Clarice, but actually Julianne Moore made a good job of it, and would do again I reckon.

I'd carry on reading the books though, as long as Harris keeps writing them. Has to be an end point, but I'd be happy with a Ripper type ending, where lecter never gets caught again.

Fava beans anyone? Or perhaps you prefer a brochette of wild mushrooms and cheeks?
Lawrence Slater

Silence was too Hollywood and too many set formula twists and turns for me that I've not bothered with the next film

I prefer Manhunter and think it stands as a better film and much more likely I'd watch it again

having said all that I can't remember the last time I went to the cinema but I might go if I can get our local (former) art-house cinema to run the 20fps version of this as I've never seen it - http://eurekavideo.co.uk/moc/catalogue/the-passion-of-joan-of-arc/
Nigel Atkins

I saw the manhunter version after the A.H. version so i was. Bit unimpressed...but considering the hollywood formulas id perfer the series stays where it is and left untouched

But rest assured... Hollywood will remake the manhunter silance of the lambs series once agian, and.like all remakes... It will truly suck to the mega 10 power ..red dawn, total recall miami vice to name a few recent ones

For get the beans and scotch... Eatting your own brains sauted in olive oil and mushrooms in the julian moore version got my icky responce amped up

That said... Id love to see the prequel of wild bill and the transformaion of lecters conversion and acceptance of his true nature... I think that would be a great film in the right hands

Prop
Prop and the Blackhole Midget

How about it Prop? Lecter for President?
Lawrence Slater

Hi all,

Quick update...

1) Have cleaned, oiled, dissy. Found a small nick in the accuspark module lead. Might be part of the problem. Weights, springs all there. Have cleaned up old points and put them back on. Cleaned and oiled base plate moves freely.

2) Vacuum seems to be working. If suck on tube that comes out of vacuum then spring connecting to base plate moves. If push base plate round then can feel change in air tube.

3) There was a dodgy bit in the earth lead insulation that goes from the base plate to the dissy body. Have put some tape over this and hope this will do the job.

In short, dissy seems to be as good as i can get it.

Will put it on today and static set it. Fingers crossed this will now be working better. Keep you posted.

Dont know about manhunter, but certainly like a nice bottle of chianti!!! hahaha.

christian wilson

>>Found a small nick in the accuspark module lead<< you saw the John twist video then(?)

>>dodgy bit in the earth lead insulation that goes from the base plate to the dissy body<< this and above could easily be the cause of rough running (it might not be but as soon as I see igniter head and rough running I think of those delicate leads)

Nigel Atkins

Hi Nigel,

No i didnt see the video, couldn't find that one. However, i did see the ones on...

static timing.
matching dash pots.
su carbs.

Weather and dark stopped play so will have a go during week.

Cheers
christian wilson

Remember christian,

Static timing is only used to get the engine started,

once its started the engine must be timmed dynamically with a timming light on the engine marks... If you drive the engine with static timming you can do some serious damage from a blown head gasket to burnt valves to holes in the top of the pistons

I do not understand this fasianation with static timming... Dosnt everone have $12 to purchase a cheapo timming light from ebay or discount tool saler....or do people actuallu belive they can blink that fast while watching the timming marks

Prop
Prop and the Blackhole Midget

Here is a timing light on ebay for less then $5...good luck
O
http://item.mobileweb.ebay.com/viewitem?itemId=290816933739&index=0&nav=SEARCH&nid=64445091680

Prop
Prop and the Blackhole Midget

Hi Prop,

No probs i have a strobe light. Just use static to get started and check dissy is working. Once going will check using the strobe.

Dicing with death again is always fun!! Thanks for the pointer though.
christian wilson

Christian,

145 New Shop 04 19 11 (igniter head delicate wires) (from 2:30) http://www.youtube.com/watch?v=dZFCRf_2c1E

53 Allison Ignitions http://www.youtube.com/watch?v=Bmp8QimgGkI

155 New Shop 06 09 11 (diagnostics) http://www.youtube.com/watch?v=WXOQl_rWJHI


Nigel Atkins

Hi all,

Just a quick update. Put old points on and retuned as per lawrences suggestion.

Result. No surging in revs. Seems to be running much better and smoother.

However, cant seem to get idle to always return to 800 revs. Set it on idle and seemed good. When driving it though, sometimes it drops back down to around 1200 and sits there, sometimes down to 800. Seems wierd. No consistancy.

When test driving.... Accelerated brilliantly, nice and smooth. However, when slowed down to stand still after a hard acceleration it cut out. Did this twice. Too damn cold and dark for anymore fiddling.

There is a garage in lewes (near me) that has a rolling road. May take it there and get them to see if they can work out whats going on when running on the rolling road.

Thanks for all your help.

Nigel, yep maybe ur right and the leads where at fault on the accuspark module. Old points seems to have stopped surging problem. Thanks for the links.

Lawrence, many thanks for the offer of having a look at it. Thats very good of you.





christian wilson

Could the inconsistent idle be caused by a sticky throttle cable. Next time it does it drop your heel over the top of the pedal and gently pull back, or try blipping the throttle.

Just a thought.

Ian
I Ball

throttle cable check is a very good idea and that pedal hinge and pivot points are lubricated (as per Driver's Handbook) and carbs linkage

I had a bent organ foot pedal hinge pin once that caused a few problems and bit of finding

you could have worn carbs

don't rely too much on the rev counter being 100% accurate

I'd suggest before going to a rolling road your car is fully serviced to make sure it's up to a rolling road use
(including new oil and filter and air filters) but I'd take along a new rocker cover gasket and ask for the tappets to be set, points and plugs checked (or do it yourself beforehand) then have timing and mixture checked
Nigel Atkins

Hi Christian

You need to check that the su jets are returning right back when the choke is in. To do this, pull the choke out and you will see that the jets are pulled down under bothe carbs, enriching the mixture. Next, put the choke back in and the with a finger push both jets up. They shouldn't move but if they are dirty, they may stick down slightly and that'll mess up your idle mixture. Make sure that the choke cable is lubricated and doesn't stick as you'll effectively have the idle running high if the cable won't allow the choke to reset. The choke makes the mixture rich as described above and also increases the idle speed so it's essential hat it doesn't stick.

Just one other thought, you are sure that the throttle clamp that you loosen to balance the carbs, is tight? If not, your car has a fluttery butterfly and that might explain the erratic idle.

I'm happy to talk you through some checks on the phone, just email and ill send you my number.
Good luck.

Robin
Robin Cohen

Problems with idle can be worn spindle shafts letting in air.
Easy to check by feeling for slack.
If present just replace the spindles (from Burlen fuel systems)- the brass shafts seem to wear before the aluminium castings fortunately !

R.
richard boobier

It seems the one consistancy is the 2 minute mark of driving...you mentioned that several times it runs good and with in 2 minutes its an issue

Good job on figuring out the accue spark was a source of a problem

Prop

Prop and the Blackhole Midget

Hello and thanks for your comments.

I Ball,
will look at cable and pedal. Seemed good when playing with carbs. But definitely worth a look.

Nigel, Robin and Richard.
I have stripped down the carbs and rebuilt using a SU rebuild kit. Replaced spindles and butterflies, Jets, and petrol valve and floats. I put some vaseline round the end of the spindles just in case they were leaking as per an earlier comment. The only thing that i noticed was that the carbs had GY needles, rather than the AAC ones specified in the owner manual. Is this a problem? Should I change them before I get it set up on rolling road? Why would the carbs have GY needles?

Prop,
Yep, know what you mean...to coin a phrase "it makes me want to buy a double wide and put the fridge on the front step" hahaha.
christian wilson

you'll need someone like FRM who knows which needles went in which cars as standard or some one with a table of SU needles

the wrong or correct needle makes a big difference to how the car runs

perhaps your carbs are not original to the car and possibly from a different car all together (or even not a matching pair?)

before going on a rolling road it's best to have the whole car fully serviced and running as well as it can to save damage on the way there
Nigel Atkins

Hi Nigel,

Did wonder if the carbs were off another car!!

Looking at part numbers...

Dash Pot AUC1357
Piston AUC1432
Needle GY
Carb Body AUC870, AUC871
Damper lid AUC8103

Bodies are different numbers, but rest match up. Will try and find out what they are from. Unless someone already knows?

Thanks.


christian wilson

what are the numbers on the float bowl tags?

is your car a UK model?
Nigel Atkins

Hi Nigel,

Float Bowl AUC 1310

Both same number. Yep, is a british car.
christian wilson

If you google Windsu you can down load a free bit of software to compare needles etc - more f you pay a license fee.

The GY are weaker from about mid way to full extent.

If your car is standard I would run with standard needles to start with.

R.
richard boobier

Christian,
I was thinking of the metal tags held by one of the three screws that hold the float lid on each bowl they'll also have F and R on them for Front and Rear

according to the SU web site UK Midget '73 &'74 has AUD 662, which only show AN needle - http://www.sucarb.co.uk/CarbEssentials.aspx?ProductId=10993

of course the golden rule is always to start at (the relevant copy of) the Driver's Handbook which will show, if the carbs are original spec, the carb needles and spring type

my copy shows weak needles as GG and rich as H6

the link Richard has given will show the difference in needles
Nigel Atkins

Christian

this link might help you with SU needle specs & carb specs

Ed

http://mgaguru.com/mgtech/books/pdf/Tuning_SU_Carburetors.pdf
Ed H

Nigel, Richard and Ed.

No tags on the fuel bowls i am afraid. The owner manual handbook states..

" Engine type 12V 778F Carb Needles AAC.
Carb Springs Light Blue
Carbs types Twin SU type HS2"

Have ordered new neeldes from SU but awaiting parts. I ordered GY to replace what was there. Guess could ring them and see if they have AAC ones.

Will have a look at the other sites tonight.

Many thanks.
christian wilson

Like lots of long threads, the plot gets lost. Post number three or four in response to the question "has this problem developed or always been there", the answer was:

<<Was working fine but has slowly developed this problem>>

So why should the finer points of su needles selection become an isssue? Still sounds more like something has gradually worn, or split, cracked or fallen off!
Graeme W

Graeme,
since that question was quite rightly asked other changes have been made and things moved on

OP was also after a good tuner in the Brighton area

Christian,
as your good book says AAC for the 12V778F* engine then if you think the carbs look original that's what should go in if the engine and other bits are standard

you are now finding how information can be confusing with even the SU site giving misleading information about what years their carbs went on to our cars which is why I always suggest [b]starting with[/b] the original factory publications relevant to the model for [b]standard/original[/b] parts rather than the many catalogues with errors - certainly numbers and stock reference may have changed but it's best to start from a reliable base

treat yourself to this DVD - http://www.rimmerbros.co.uk/Item--i-HMCC3009DVD

I think perhaps (only possibly) photos at various angles of the engine bay may help generally

Nigel Atkins

Greame is correct.... We have lost site of the orginal issue

This was a slowly evoloving issue of rough running that resulted in back firing....

The question was asked about the backfiring

... Is it popping on deceleration or is it backfiring thur the carb. Or is it a shot gun blaste thur the exhauste

At this point ... Thats a big clue, but the question was never answered

What say you ????

You said you checked the wieghts and springs inthe dissy and you said they are okay... How dod you check the springs were not worn out and maybe became to weak and springy???

Prop

Prop and the Blackhole Midget

Prop, Graeme,
(btw Graeme I wasn't trying to be shirty with you (now or) in my previous post just badly written)

I've reread Christian's posts here and the problem is now inconsistent idle and engine cuts out when coming to a stand still after a run

for some reason Christian has GY needles in his carbs, as he's had the very good sense to purchase (and hopefully reads) the Driver's Handbook that tells him IF his carbs and other items are original/standard then the needles should be AAC

the problem has changed from the original post (a bit) as a lot of work and changes have been made since

the current problem seems as if it might be a carb/needles/mixture/settings problem possibly with a bit of timing thrown in - but of course other issues might also be effecting or causing this

Nigel Atkins

Thanks Prop.

My original dizzy didn't have a vacuum advance and the car popped an awful lot on over-run. I replaced the dizzy, connected the vacuum and although there is a little popping it does't sound like Gunfight at OK Corral any more! Which to me points to distributor issues.

So many problems I have had with "classics" (when they weren't old enough to be classics) came back to links with the distributor. My current Sprite only let me down on the road once (so far) and that was where the spark-lead was rubbing on the steering column and shorting out from time to time.

What ever Christian's problem is, it is significant that it has become worse and hasn't been there from Day 1. Something is deteriarating.

Christian: are you a member of your local MASC group? There surely is someone there only too happy to open up the bonnet with you. There's nothing like someone's car not being quite right to totally empty the monthly pub meeting out into the car park!
Graeme W

Nigel: our posts overlapped. No offence taken mate. We all have views based on our own particular experiences. As you will gather, mine nearly always came down to ignition!!!!

It's just with SU needles I would have thought it would have been consistenly good... or bad..... and not changed.

Graeme W

Graeme,
Christian had other issues including possibly one of my hobby horses of an electronic igniter head with a nip in the delicate lead which could cause all sorts of running problems

I've noticed a lot of people that have problems with igniter heads it's down to the installation rather than the unit that's why I posted the links to the three John Twist videos that include the subject

we've also been through the dissy (the oft missed oiling and lubing but as Christian now has a DH that'll be in there) and he's checked the vacuum

I've suggest photos of Christians engine bay to hopefully pick up on obvious things that might have been missed

a lot of things have been covered so it could come down to something annoyingly simple - or of course something not checked yet!
Nigel Atkins

Firstly let me apologise if i have ruffled anyones feathers, it was never my intention and am very grateful for all your patience, advice and comments.

As I have mentioned before, I am very new to dealing with mg's, SU and twin carbs. I appreciate this thread has now become very long and therefore hard to follow. Just wanted to keep it all in one place rather then have several threads that were really related (maybe just by my lack of experiance).

It seems to me, in view of your suggestions, that there isn't simply one issue here. More likely a combination of worn parts, lack of maintenance, and a lack of experiance on my part. Learning curves can sometimes be very steep. I know your collective knowledge and experiance is far greater than mine.

Anyhow, apologies aside. I will do a detailed recap of what I have done and post this tomorrow. Can start a new thread if this is better.

The reason i mentioned carb needles was that it was suggested that one needle may be bent. The bent needle jamming up, sticking, one carb. I have overhauled the carbs and I dont want to pay for the car to be set up on a rolling road if it would ultimately run better with the right "according to the manual" needles in it. Seems logical to have it set up with right needles in it. Thats all. Spoke to SU and am ringing them again tomorrow.

Many thanks, Christian.









christian wilson

no feathers ruffle (by you anyway :) ) carry on as you are

it may may be more than one issue (or it might not)

this is one of the reasons I always suggest a staged 36k-mile service for the whole car as it picks up faults and prevents them

the carbs and engine are favorites for early treatment but are really low on the list of importance on a car, so it cuts out when at a stand still that what the most modern cars do

important systems and items on the car are brakes, tyres, suspension, lights and windows

in case I haven't offered before I've got some notes for those new to classics from a non-technical, non-mechanic, me, based only on (sometimes) expensive experience and a slim update for the DH, email me if you want any, I'm not offended if you don't
Nigel Atkins

according to this - www.ahcso.com/pdf/SU%20Models%20&%20Part%20Nos-Sprite.pdf

the GY needle is standard to the 1962/3 1098cc (CG) Spridgets

and shown as such on SU we site http://www.sucarb.co.uk/CarbEssentials.aspx?
ProductId=11008

and confirmed in terry Horler's book - http://books.google.co.uk/books?id=RQK6R2Y3SZ8C&pg=PT8&lpg=PT8&dq=original+sprite+and+midget&source=bl&ots=yhO8WALiae&sig=Ak2LCNDj0ZztCwfrkepyM5i1LKE&hl=en&sa=X&ei=pP2_UPfRLI_L0AW9rIGABQ&ved=0CEIQ6AEwAw

Christian,
does your engine breather vent to your carbs via a Y-piece as in this photo? (now you see why I suggested photos of your engine bay to pick up quicker on things like this)


Nigel Atkins

bl**dy computers

and shown as such on SU we site http://www.sucarb.co.uk/CarbEssentials.aspx?ProductId=11008
Nigel Atkins

now I've cracked the SU search (only marganally easier that Archives here) have this link before I lose it - part number AUD 1468 -
http://www.sucarb.co.uk/ProductDetail.aspx?pumpsearch=&Id=33657
Nigel Atkins

Christian: no feathers ruffled. This is a typical thread by all accounts:

Starts off focussed
Get some useful albeit incomplete advice
Handbook gets mentioned
Lawrence mentions either/both motorbikes and/or some ancient piece of rock music which has slightly modified words to suit the circumstances.
Prop puts in his fourpeneth
Advice gets focussed again (partially)
Go to "start" and repeat

The problem is I guess that rarely does anyone go back to the begiining and read it all through so the logical pathway does get lost. You problem touches the "I've had that so I know the answer" bit in all of us so everyone is an expert and likes to help by expressing an opinion.
Someone is going to be right, but a lot of us will be barking up the wrong tree!

Yes, a summary would be helpful -it's a lot to read otherwise.
Graeme W

If there's any barking up the wrong tree,

"Who let the dogs out (woof, woof, woof, woof)"



Lawrence Slater

Forget the needles size for now, it's a red herring for the moment.

christian said.
"Just a quick update. Put old points on and retuned as per lawrences suggestion. Result. No surging in revs. Seems to be running much better and smoother. However, cant seem to get idle to always return to 800 revs. Set it on idle and seemed good. When driving it though, sometimes it drops back down to around 1200 and sits there, sometimes down to 800. Seems wierd. No consistancy."

As others said following that, there could be air leaks or bent needles.

So step one.
Remove dashpost and inspect needles. Doesn't matter if they are the wrong needles at this stage, as it will run either weak or rich, but it will be consistent at least. do a drop test on pistons to see if the pistons fall correctly. If not ---

step 2.
centralise needles in jets. if this doesn't solve the problem, step 3.

step 3. Look for air leaks, which may be at spindle, or in manifold.

Report back.

In the meantime, woof woof woof. "Crazy! I mean like so many positive waves maybe we can't lose! --- "
Lawrence Slater

.... and ensure the correct oil is in the dashpots. Without that they will lift too quickly!

What's the correct oil? My HANDBOOK (da-dah!) says "engine oil" but I have seenother references to "3in1" spec oil. You can also buy little pots of "SU carb oil" which presumably is one or the other repackaged with bigger margins. As I'm not sure, I use one oil spec in one and one spec in the other.... that's why I like twin carbs (really?....nah!)
Graeme W

20/50 engine oil works fine, but so does 3 in one. Just about any oil will provide damping, and eliminate that as a potential cause of the erratic tickover.
Lawrence Slater

Graeme,
after you putting go back to the beginning I went back to the beginning and reread all of Christian's responses which is why I got back to photos may be required and the GY needles are not the needles usually used in the standard carb - yes we know this because the good book says so :)

a reliable source of accurate information (of a standard car when it was new back in the day) is the relevant DH and quite often is not web sites not even SU

as for what goes in the dashpots I can give you loads of suggestions from other people but Christian has already said he's using SU SAE 20, I might put a thread up to get some debate going :)

Lawrence,
IIRC the needles should have checked as they're new from the carb rebuild and viewing of John Twist videos as should have been the drop test as matching carbs

leaks I can't remember being covered

that quote I had to look up, I thought it was a song lyric
Nigel Atkins

Nigel, one was from a song, one was from a film.

The first was in reference to the thread going "off message". The 2nd was a parody of the first, intended to boost morale. LOL.
Lawrence Slater

Meow, meeow, moew, moew ....its dance fever thursday.

A bit*h playing with her p*ssy

What ???... A female dog playing with her favorite kitty cat...

Just a response to woof, woooof wof

Prop
Prop and the Blackhole Midget

Now all the dogs will be chasing tails Prop. lol.
Lawrence Slater

how can you ever follow a Prop post(?)

L,
I recognised the song lyrics but not the film quote so I had to look that up
Nigel Atkins

Woof, woof, to one and all. Kelly's hereos...donald sutherland...eat ur heart out.

Here goes.....

Distributor. Lucas 25d4.

Have removed it. Cleaned it, twas very dirty. Lubed it. Checked weights and springs there.

One spring was stretched. Replaced springs.

Vacuum...sucked on air pipe and it pulls plate round a tad. If spin the dissy then can hear vacuum move.

Accuspark electric module removed. Old points, cleaned and set and replaced. Condensor replaced.

RESULT...found a nick in accuspark module lead and a fraid bit on dissy earth lead that goes from plate to dissy wall.

No more erratic surging in revs. Was not an original problem but one that developed along the way!!! Assuming nick in the leads.

SU Carbs. Twin SU type HS2.

Removed carbs. Cleaned thoroughly. Rebuilt with SU kit.
Replaced Jets, Petrol valve needles, seals, damper springs (light blue), butterflies, spindles, a bent mixture screw. New gaskets from manifold to carbs. Ordered new needles from SU, one looked worn. GY needles wont come till january.

RESULT...look nice and clean!!! Have learnt a lot about su carbs, tried everyones patience :)

Now to the crunch....

Idles o.k. and accelerates smoothly...original problem of popping on overun gone away. I am assuming this is due to dissy, points, now clean and working better.

Problem at moment is idle when driving seems to vary from 800 and 1200 revs. Twice it has cut out when slow to a stop after hard acceleration.

Think this must be carb related. But hey what do I know...hahaha..."positive vibes and gold bullion all round".

Will follow lawrences pointers and let you know...hope this has cleared up the thread. Crazy!! indeed. Will now leave you in peace until have more info.













christian wilson

Good wrok getting this far. Two thoughts on the variable idle:

Variable idle as you describe is a classic symptom of air leaking in the spindles. usually there is quite a bit of wear in the carburettor body as well. Did the rebuild kit include bushes for the body or oversize spindles, or was it just new standard size spindles only?

Does the throttle plate have an over-run valve in it? These can leak and cause this too. I've seen these soldered up in response, but the simple way is to replace the plate with the plain type with no over-run valve.
Paul Walbran

Normally ... Popping on decelaration is due to a lean mixture...this can happen from a vac leak as paul suggested...my guess its been lean for a while and with you doing a basic rebuild may have corrected some of the leaking
No one has mentioned it ... ??? But have you tried to use the lifting pins to check that the carbs are set corrctly...sometimes when these carbs wear they need to be richend beyound the drivers / haynes manual

But id give those pins a lift and see what happens

If a slight momentary lift in rpm then back is good

If the engine stalls .. to lean

If it races for a long time its too rich

But.. yeah, im still thinking vac leak somewhere... Spray down the running engine with carb or brake cleaner... ( oh gez did i say brake cleaner...lol) and listen for a rise in rpm... If it rises you found your vac leak

Check the screws on the intake manifold, those can come loose... Weve seen it here before... So dont feel embarresed if thats the case... Cause we will definatly make fun you for that

Prop
Prop and the Blackhole Midget

Hi Paul and Prop,

Paul, the kit came with spindle bushes, but didnt know how to get the old ones out. Do the bushes need to be drilled out, or can you pull them out?

Prop, will check for leaks and lift the carb pins and manifold screws. To err is to be human. The more laughter the better...thats what i say. They are not wrinkles...just laughter lines!!!

cheers.
christian wilson

I ream the carb bodies to size then fit new bushes. It's important to maintain alignment between the two sides of the carb, so drilling can lack the required accuracy. If you haven't got the gear to do it, it's best to get it sone at a machine shop.

My preference is to go for oversize spindles if available, saves a lot of work. These spindles are aftermarket ones, .008" oversize which very few carbs won't clean up at.
Paul Walbran

Having just caught up - I can't have this excitement EVERY day, not at my age!

.... picking up on Lawrence's point about dashpot oil:

I seem to remember wayback when discovering what made things run and what broke them, that too thin (or no) oil in the dashpots allowed them to lift too quickly. This upset the "footdown" reaction and caused hesitation and stalling when you tried to accelerate. It didn't seem to upset tickover.

Not being pernickety Lawrence, just wondering whether my recollections were right.

I'll see what the handbook says too! :-)
Graeme W

Yup your right Graeme, but I've used 3 in 1 before and whilst it does allow the pistons to rise to quickly, and give you a "flat spot" as it used to be called (maybe it still is), it won't likely cause surging on tickover, or "hunting" as that used to be called.

It's still more likely to be an air leak as described below. Or even remotely possibly, timing if it's too far retarded I seem to remember. Points in, and timing set to static should have eliminated that, and that leaves an air leak.

Lawrence Slater

Christian: if you try Prop's suggestion and lift the dashpots you do it using a small vertically postioned pin on the car underneath the dashpot. But be careful to lift only the tiniest amount - I think less than a mm. Otherwise the results are not a true representation. I find unscrewing the dampers from the top of the pistons but leaving them in position lets you see the dashpots lift on the pin.

Have you tried a Colortune? (our aim is to have you totally skint at the end of this thread!)
Graeme W

Hi paul,

I do not have the equipment, reams, or the know how to attempt the bush replacement. Do you know where i could get an oversized spindle from? Did a quick google but to no avail.

Will have a go at carbs tomorrow.
christian wilson

Christian,

Before you pull the carbs apart... SpraY the spindle area with wd40 withe engine running and agian at high sustained rpm... If the rpm des not increase by a 200 or so rpm... Then its not the spindle

I hate to disagree with paul as i have alot of respect for him... But its so rare that the bushings are worn on the carb bodies ...its almost always the spindle its self

If it is the bushing inside the carb bodies... Id just get a good used set of carbs and rebuild them with your new rebuild kit.. As the likely hood of 2 sets of carb bodies beening worn in the bushings would be almost lottery odds


Prop


Prop and the Blackhole Midget

I suggested replacing carb spindles about 3 weeks ago (14 November) as the symptoms pointed to air being drawn in. I also commented that more often than not there is sufficient improvement gained by just renewing the spindles, rather than getting involved with bushing and reaming.

However, if you are of a DIY nature and have the patience, there is a method of replacing and reaming the bushes described here:
http://chicagolandmgclub.com/driveline00/1001/jasw.html

Guy W

Yes you did guy... I belive we are now at the point where we begin the entire process all over agian... :P

Seriously dosnt someone have an issue for us to work on, this one is getting long in the tooth

Prop
Prop and the Blackhole Midget

Hi Guy and Prop,

Thanks for the link Guy, and your original post. When i put the new spindles in I did put a lot of vaseline around the end of the spindles. I believe u suggested this as a way to check if they were the problem (to temperarilly remedy the leak).

I am going to have a go at the carbs tomorrow. Will spray away with wd40 prop and guy. Hopefully will not need to replace bush but just wanted see what was involved. The spindles in the carb kit were standard size i assume.

Let you know how i get on. As usual thanks alot for your help. Hope ur all having a great weekend and you get something new to get your teeth into.

christian wilson

Prop, you are right. What goes round comes round!

Not sure if this would work but you could try making up wear in the casting with epoxy filler (J B Weld)
You would need to degrease the casting with meths, oil the spindle so it doesn't stick, and inject the resin into the gap with a syringe. Might be worth a try.
Guy W

You should see my old twin carb bodies then. Have to be an big oversized spindle to fix those babies. That was one reason I dumped them and went HIF44 mode.
Lawrence Slater

Mmmm, I've been operating on stock I bought years ago, but I can't see anything around for the HS2 either, so it looks like when I run out that's it. HS4 and HS6 oversize no problem, but not HS2.

Prop - I would have found 80%+ of bushes to be worn.

The test to see if the bushes are at fault is simple: grab both ends of the spindle and wiggle it the horisZontal plane then the vertical plane. If there's nop movement then it will be OK. If therer is movement, then it needs re-bushing. As per Guy's suggestion, air leaks though spindles are the no 1 cause of not idleing consistently at the same speed. (To be more specific: Each time you blip the throttle it settles to a different idles speed). If you have this symptom and you get movement in the spindles doing the test I've described, there's your answer. I have yet to find a case like this that wasn't cured by removing that play.
Paul Walbran

I was going to do a separate post on re bushing HS2 carbs but didn't get round to it! Most time, it's the brass spindle that wears. I recently bought a set of old ones from beaulieu auto jumble. They were filthy and seized and were intended to be used to test a home made stepped cutter to re bush my current carbs. In fact they cleaned up really well and again, only spindle not body wear. However, if it ain't broke, it needed fixing.

Of course, there is nothing wrong with the current ones on my Midget! new spindles when I built them were needed. The running on issue turned out to be octane and compression related.

To cut a long story short, I made a cutter from turning down a silver steel rod and sliding the cutter over a 1/4 length of silver steel. The 1/4 rod ran through both existing holes and guided the cutter to the required depth. turn round the carb and repeat. This self aligned the holes and allowed me to cut only to the depth of the bushes rather than right through. The cutter was made on my lathe, the actual cutting in a hand drill and worked a treat! So, I now have a shiny, rebuilt set of carbs as garage trophies, one small, if expensive victory for home fettling! I some photos of the cutter and the operation that I should find if you're interested.
Robin Cohen

Robin,

Would like to see your pics.

Is the cutter an inserted bit like a boring bar or formed on a reduced section of the rod (I see you specified silver steel i.e hardened after machining)

Been thinking about making one myself.

R.
richard boobier

When i rebushed my HS4s.. i think i only paid $15 for the reamer at a local machine shop that sold machine tools

Prop
Prop and the Blackhole Midget

I spoke to Burlen Fuel systems and was clearly told that ideally, you do not pass a 1/4 inch reamer right through the carb body, you ream only enough to allow the bush to push in up against a shoulder. The carb body is actually quite a lot wider than the supplied bush and reaming right through to 8mm (well 7.96 for a push fit) would mean that there is a lot of clearance for around 5 mm each side between the bush and the carb butterfly.

The reason that I made a cutter and the reason that this was a bit tricky, was aligning the holes but not drilling from one side through to the other.

Photo attached of the cutter:



Robin Cohen

The cutter on the 1/4inch silver steel shaft which is aligning in the SU. The cutter cuts to 7.96 mm for a push fit bush (made with trial and error on the lathe, silver steel cuts fine with a HSS tool).

Robin Cohen

This thread was discussed between 10/11/2012 and 10/12/2012

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.