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MG Midget and Sprite Technical - help me get my engine running properly

Hi everyone,

I've currently got the midget all back together and running with a new Maniflow manifold and a repaired inlet manifold as it turned out to have a big crack in it.

last week it was running but idling at 3k and a bit down on power, so today I have stripped, cleaned and re-gasketed the carbs to cure any air leaks and have tried again.

now it won't idle at all :D

it'll start on the choke but runs very badly and will eventually stall after about a minute. I can run it by holding the throttle open, but again, it's running badly.

the plugs are very sooty and there is obvious excess fuel on them, so it's clearly running very very rich, but how do I sort this?

the timing is also almost certainly out as I have move the dizzy when trying different caps on it.

it's a 1275 from a Marina, non vacuum advance dizzy.

I'm stuck as I don't really know where to start, as I can't seem to time the engine if it's running too rich and can't get the mixture right as the timing seems to be out :)

cheers, Phil.

phil near bristol

Where near Bristol are you ?

How far from Clevedon ?

May be able to help a bit if required.

R
richard boobier

i'm in Claverham :)
phil near bristol

got a Haynes? It should all be in there...start with the carbs, set the jets flush with the bridge then screw them 2 full turns (12 flats) upwards. This should be good enough to get it running. Set the dizzy using the procedure in the manual - turn by hand until the test light lights, then back a bit - and then fine tune from there. (all if my memory's OK today !).
David Smith

Just a couple of quick things.

Im assuming your running 2 SU HS2s carbs

It could be the carbs just need a good cleaning and adjustment

make sure the carb pistons are moving up and down freely .... meaning that the needle is centered properly...if its not the piston can hang up thus releasing alot of fuel, also the inside of the dash pot that houses the piston can get really dirty and hinder the piston...If so, DO NOT USE abrasive, on the piston or inside of dash pot...Acetone and scrubbing...All though I do use a green scouring pad but nothing stonger

have a look at the carb piston springs, that they arnt binding up or corrodied...these things are vary sensitive and help control the pressure on the piston...so if the spring is working harder/stiffer it can be an issue...just dont give to the temptation of pulling the spring apart to make it longer

Make sure the dash pots are topped off with 20/50 motor oil,


look at the linkage...its fairly common for linkage to bind esp. with the little tab washer with the spikey points on the ends of both shafts

cheak the little nut on the bottom of the carbs for proper fuel mixture...run it to the top (bottom of carb) then back it off 12 flats...(I always paint one flat red on both carbs while its at the top before backing it off.


http://www.mintylamb.co.uk/?page=sutune.htm

Prop
Prop

Have you checked the fuel pipes and petrol tank to make sure there's no gunk/sludge getting in?
rachmacb

Phil,

I'm having computer problems at the moment so running on a spare - e mail difficult to access etc.

Phone me if you need any help 01275 872585 you don't seem far away.
Do you have a timing light etc ?

R.
richard boobier

all fuel lines and pump are new, tank was cleaned and i put half a gallon of fresh fuel in this morning.

the pistons move up and down ok - moving them up when the engine is running makes the revs rise a lot, a 'too rich' scenario according to haynes.
The springs are good - I checked a few months ago, the linkage is also good, I did that a while ago too.

timing:

can someone remind me how I check the engine is in the right place ? I did the trick of putting apencil in the spark plug hole then moving the engine till the piston was at the top, but I'm not 100% it was at the firing stroke - the rockers at the 'back' of the engine (no.4 piston) were 'loose' so did I get it right ?

will give the carb nuts a spin and see whats what.

phil near bristol

richard: I have a timing light (which I think works) but I am at a loss as to how it's possible to see the pulley or the marks on the timing chain cover when the engine is in place :)
if i'm still stuck I might give you a call tomorrow

Prop:

I span the nuts all the way in then out 12, but it still ran poorly, so just to see what would happen, ran them all the way in and started the engine - it idles ok like this, but backfires through the carbs under load (trying to pull away with the handbrake on)
phil near bristol

dug out the timing light, it does work :)

I can't see the marks on the timing cover,so all i could verify is that the advance mechanism in the dizzy works, as the pully 'moves round' when i rev the engine.
phil near bristol

Phil. You can see the timing marks by looking from underneath the front panel, viewing the crank pulley through the cross member. you may have to lie down to do this.
The rockers on the front cylinder 1 should be the ones which are "loose" at the top of the stroke, then look at the rotor arm and see that it's pointing to the correct segment of the cap. You can fine tune it from there. I'd use something a bit more substantial than a pencil to feel the piston, because if it breaks you could be in real trouble.

Bernie.
b higginson

bernie:

cheers, I can see the three 'teeth', what an awkward place :) but when I shine the timing light on them, I can't see the pulley mark - i'll stick a of bit on paint on it and see what happens then.
phil near bristol

Phil,

If its running, the timing must be roughly O.K, so set up correctly with the light - its difficult to see - yes lying on the floor is required ! I have a bottle of the old tipex to mark the pulley and mark the teeth.

Have you checked the condition and setting of the points - corect gap is essential (assuming your not electronic).

Give me a bell and I should be able to get away from my DIY ! Would be nice to meet another spridgeteer in this area - seem thin on the ground.

R.

richard boobier

I have had one thought - the engine was orginally in a Marina, and I had to swap over the timing gear and timing cover, but I'm pretty sure I used the Marina pulley - would the marina have had the timing marks in a different place ? 'cos if it did, it's going to be tricky to time it up :D
phil near bristol

richard:

yeah, it runs, it now even idles, though a bit high - randomly twisting the dizzy I can get it to idle at about 900rpm, but it doesn't 'feel' right, it seems happier at 1100rpm.

will check the points etc tomorrow, I do have an electronic kit to fit, but I don't really want to introduce another variable until I have everything running smoothly.

phil near bristol

Phil as you are aware both ignition timing and mixture need to be set correctly for the engine to run spot on.

The very first thing you should do is to set the timing correctly. This is simple to do normally and once done it can be forgotton and the carbs can then be set up and sychronised. Unfortunately for you you have fitted a Marina pulley and a Midget front cover which do not correspond with each other for top dead centre. You need to identify TDC on the timing marks and pulley by perhaps a DTI through the plug hole or similar.

If you are unsure of how to set the timing correctly see here. http://www.mgcars.org.uk/mgcc/midgetreg/workshop.shtml then click on ignition system for a full description. I note yours is a non original distributor so it is very important that you use the 32 degree at high revs method as described to set your timing correctly.

Once you get that correctly the next most important thing is the sync of the carbs. That means both carbs should suck the same and remain the same when the throttles are opened. I have seen dozens where the owner has set the suck on both equally at idle yet as the throttles are opened the linkage is not set correctly and the throttles open at a slightly different time.

Once these are set hopefully setting each mixture screw ought to be a doddle. :)
Robert (Bob) Midget Turbo

so the best course of action is to get piston 1 at TDC on the firing stroke then mark the pulley against the correct 'prong' on the timing marks ?

then go from there ?
phil near bristol

Correct.
Dave O'Neill 2

cool.

next question: to set/check the advance I assume I need a mark on the pulley at 32degrees ? if so, is there a magic way to measure and mark it while the engine is still in the car ?

or can i just set it at idle and hope for the best ? the advance does work and seems quite stable, I just don't know how much it's advancing :)
phil near bristol

Phil I take it you don't have a Haynes or other workshop manual (you didn't say), but do you perchance have the Driver's Handbook?
Page 44 - "Static timing 7 degrees BTDC"
After that the bob weights and vacuum will sort out the rest, they won't be far out. If you have the right cover the three pointers are 0, 5 and 10 degrees.
David Smith

David:

yeah, I do have haynes, both mg and marina versions :) its just they are so vague :D

I have the right cover, but on the wrong engine :)
phil near bristol

Phil,

As mentioned above by Bob, you MUST sort out and set up your ignition timing before you do anything else. If you have accuratly determind the TDC, then set up the static at circa 7 to 8 degrees, then run the engine up and watch the timing marks move as you increase engine revs. With an adjustable timing light, you should aim for no more than 32 degrees MAXIMUM advance.

Once thsi is all OK, then sort out and set up your carbs.

Nobody has yet mentioned the manifold to head joint... This is a common fault on the Spridget and if loose, will draw air and upset the running.

Prop mentions the theoretical 12 flats down set up for the jets. I have found on a 'worn' set up, this is too much, settling for closer to six flats down, (each vehicle will be slightly different).

Oh, my preferance for dash pot oil is a cycle or sewing machine oil, not a 20/50. You can of course us Automatic transmission fluid.

Good luck.

Mark.
M T Boldry

phil,

Just an idea.

If your going to "Re-Mark" the timing on the pulley, perhaps once you have it set up to TDC and are about to mark the pully.

Instead make a pointer with the 3-5 settings (that match the pointer below) and mark the pulley so you can see it from up on top, instead of lying down looking up

Prop
Prop

Mark - I renewed -all- the gaskets yesterday, so I could be sure that there are no air leaks :) well as sure as I can be :)

prop - that makes sense :)
phil near bristol

If there were air-leaks, you'd expect it to run weak...

Check your chokes are returning to the fully up position... give them a gentle push with your finger to check (pull choke cable on then release to off, first).

A
Anthony Cutler

Phil the easiest way to mark 32 degrees or any amount of degrees is to duplicate the 10 degree marks. measure the 10 degrees and mark that another twice around the pulley that should give you 300 then simply judge a couple more. This is far superior to HOPING that your dissy is set up to 7 degrees static equating to about 32 max. :)
Robert (Bob) Midget Turbo

been busy with other stuff today, but had a quick play earlier - found tdc on cylinder 1, rockers loose, then marked the pulley and timing case where i could see it.

but when running the engine, the marks are waaay apart, I could bring them a bit closer together buy moving the dizzy anticlockwise, but too much and the engine wouldn't run.

as i didn't have much time, the engine wasn't properly run up to temp, so will have another go tomorrow.

but can I confim some stuff, in case i'm being extra dense :)


if i find tdc on 1 and mark the pulley and case (I do not have timing marks as i'm using the wrong pulley) then should the marks line up when the car is up to temp and idling ?

as an aside, i grabbed the old engine from my lockup, to confim that it has the midget pulley on it, and it does.
interestingly, the marina timing cover has the marks where the drivers side engine mount is - would be a lot easier to see :)

I may give in and drop the engine and swap the pulleys over :D
phil near bristol

Now you are talking Phil, I put a Mini timing cover on my engine along with a Mini pulley to achieve timing marks in the same position as the Marina, you could do the same by leaving the Marina pulley on and mating it up to the Marina timing cover.
By the way at idle when timed correctly the timing (flash) ought to be somewhere between 5 and 10 degrees BTDC.

How did you determine you were at TDC. I ask this simply because the piston is statioery for a good few degrees at the top. How engineers tend to find the exact point is to not the position just before the piston stop rising say 2mm from max (mark this point on the pulley) then keep turning until the piston has fallen the same 2mm (again mark this position). Now true TDC is a point that is exactly between the 2 marks. However if you fit the Marina timing cover your problem will resolve itself. :)
Robert (Bob) Midget Turbo

Sorry to divert briefly, if the marina has the timing marks on the side, what cover do I have in this pic...
http://www.flickr.com/photos/73314630@N00/3324216296/sizes/l/in/set-72157613427903240/
Timing marks in the normal (for a midget) beneath the crank position but its a later cover to allow for a tensioner. Matches my pulley. Both cover and pulley came with the engine which is a marina block that was prepped for a Minor.

Only just come in from freezing garage but I'll check what my original spec Ital under the bench has tomorrow.
Dean Smith ('73 RWA)

I can't fir the marina timing cover as it's the wrong shape for the front plate. I can't use the marina front plate as it has no engine mounts (the marina uses mounts on the side of the block)

nothing is ever simple :D

for TDC, i guessed basically :D your method sounds good, and good info on where the marks should be when strobed.

honestly the haynes manual is even more oblique than normal when it comes to this sort of stuff.
phil near bristol

I think that is a Midget cover, although I am far from expert mate.
Robert (Bob) Midget Turbo

dean, that looks like a marina cover, pics of my marina cover:

http://www.spiny.org/marinacover01.jpg

http://www.spiny.org/marinacover02.jpg

when I put mine together I had to change the timing gear from single chain with tensioner to dual chain as my front plate didn't have the mountings for the tensioner. So I then had to use the original midget cover too, but for some reason used the marina pulley (it was probably closest)

this is the smaller midget cover:

http://www.spiny.org/van_progress/2009_progress/04_april/original/april09_DSC01337.jpg

and my original front plate:

http://www.spiny.org/van_progress/2009_progress/04_april/original/april09_DSC01410.jpg

yours appears to have extra holes, so could be modified to use the tensioner ?
phil near bristol

Is it not just a case of setting up tdc - (dial gauge down bore or what ever method is favoured) marking the position on the pulley with tipex and timing as normal 13 btdc @ 1000rpm to start with.

Will get it running fairly well (as workshop manual) and allow the carbs to be set up.

R.
richard boobier

The front plate was definitely converted to take the tensioner (by previous engine owner who was intending to add it to a minor) with a matching cover with the extra bulge. I'd assumed it was a std marina cover. But if the marina has the timing marks on the side I don't know where the cover comes from. Not important - just intrigued :-)
Dean Smith ('73 RWA)

richard - cheers, I'll dig out my protractor, work out how 'much' 12 degrees is on my spare pulley then copy is accross to the one fitted to the car and see what happens next :)
phil near bristol

Phil
Once you have got TDC, measure the diameter of the pulley. Remember circumference is diameter x 22/7 ? So when you know circumference, if you want say 30 degrees , its circumference x 30/360. Measure that distance round pulley from tdc CLOCKWISE. It works for me
Graham M V

What I was trying to say was at cylinder No 1 tdc, mark the pulley with tipex (shows up well with the strobe) against the pointer on the timing cover that relates to tdc (large pointer).

Then @ 1000rpm (with the strobe) set the dizzy to 13deg using the marks (smaller pointers) on your midget timing teeth.

No measuring required.


R.
richard boobier

ah, that makes sense :)
my timing cover just has three 'prongs', is that going to cause an issue ?
phil near bristol

Richard, where does 13 degrees at 1000 rpm come from? The handbook says 22 degrees at 1000 rpm !
David Smith

On the cover, isn't it a mini cover? I use this one, removed the bracket for the pick-up and modified my backplate for the tensioner. see pic.


Alex G Matla

>Richard, where does 13 degrees at 1000 rpm come from? The handbook says 22 degrees at 1000 rpm !

can anyone confirm what it should be at idle ?
phil near bristol

ah, cross-checked with the workshop manual - the 22 degrees is for the 12CC engine with the 23D4 dizzy.
You *should* have a 12CE engine and 13 degrees is correct at 1000 rpm - with the vacuum pipe disconnected .
David Smith

David,

You had me worried there ! been rechecking what I thought I remembered ! AGE again !

But - on reflection Phil really should check the Haynes manual for the Marina dizzy setting, as the dizzy he has is ex Marina / Marina engine.

The 23d4 did not have the vac - the 22 deg was @1200 revs also and was similar to the old Cooper S unit - had one in my first Midget in the seventies - memories again !.

R.
richard boobier

ok, braved the cold and grabbed the marina haynes, this has only added to my confusion :D

haynes mentions that there were two dizzy types fitted, 23D4 and 25D4, and that both had vacuum advance. My dizzy doesn't have vacuum advance - is the serial / part number stamped on it anywhere ? i'll remove it tomorrow and have a look if it is :)

the engine itself is marked 12V - E - H363122

anyway, the marina haynes states that static advance needs to be 9 degrees, i think ... it's not very clear :)

i took photos :D i'll add them in a bit (not near my main pc)
phil near bristol

The point is Phil with the 32 degrees at high revs, it does not matter what the manufacturers figures say or indeed whether or not you have the correct dissy set the thing at 32 degrees max mech advance and it will be spot on for that dissy and curve. Any other method relies on you knowing what dissy you have and whether or not it has been modified and whether or not it is working correctly.

Don't worry about the vac advance it is only there to increase economy and plays no part in the power of the engine. However it will smooth out the idle a little as the idle tends to enjoy loads of advance. :) which is why when people set timing by ear they will ALWAYS end up with it too far advanced. The result of which can be excessive detonation and siezed engine
Robert (Bob) Midget Turbo

As Mark has mentioned air leaks at the manifold will cause rough running also - I only re-mentioned this as you say you have fitted the maniflow (great exhausts) with the original inlet manifold.

I found there was a small difference in thickness between flanges on mine that required making up unequal packing washers to get a good seal.

R.
richard boobier

richard:

already spotted that :)

http://www.spiny.org/rr/midget/march10/washer.jpg

phil near bristol

Ok first of all, 1100 rpm seems about normal for a 1275 to idle. I wouldnt sweat trying to get it to idle at 900. If you read some repair manuals they explain that the idle speed is higher for 1275cc engines. It may have something to do with the cam profile. I don't know. All I can tell you is that my car is the same way.

About the three tick marks thing. You're best bet is to get a timing light with a advance dial. You can then turn the knob so that the timing mark aligns with TDC and then look at the dial on the timing light and see how much advance you have at any engine RPM. You can even check to see what the max advance is. Even more useful is one that has a tach built into it so that you can see how fast the engine is going without leaving the engine bay (Also allows you to calibrate the old smiths tach too!)

One solution to the mixmached front cover and pulley is a kit like this one http://advanceddistributors.mybisi.com/product/0/MGB-Timing-Tape-kit-1962-1971_404918.html

That way you can time it from above and see more advance degrees without a fancy timing light.

But just for reference, on my Midget with a 12CJ/DA/H engine (stock for 1971) the timing mark appears as a 3/8"ish dimple drilled in the front of the pulley.

Did the marina have a timing chain tensioner? Just curious. To me it looks like the cover would accomodate one (not that its really needed imho).

About the dizzy. I am curious about it. I don't know if there was a picture of it anywhere, but it is possible to remove the vacuum unit from the dizzy. Some people like VA some don't. You sure a PO didn't just remove the VA from a 23D or 24D? A photo might also help identify it. Serial numbers are often stamped on the side of the unit, and model numbers are sometimes found on the top of the casting near where the VA unit would go. It may be though that you have a 45D unit (or even something else entirely).

Prop mentioned earlier something about centering carb needles. That all depends on the kind of carbs you have. HS series carbs all have self centering needles that are spring loaded and designed to gently rub against one side of the jet. It is impossible to center. Just make sure that the mechnism is not jammed or stuck and the the pistons move freely downward even with the dashpots nicely topped up. H series carbs have centerable needles.

-seth
S.A. Jones

Seth

The Marina had a simplex chain and a tensioner. You can run the duplex chain with the tensioner for the best of both worlds.

Both my current timing chain cover (from marina block) and original Ital cover have the timing marks at the bottom. There's another thread in the archives with a cover with the marks like Phil's described as a metro one - So Phil your cover might not be marina original ?

My std 1275 idled just under 1000 with crappy orig distributor and points. I could get a very nice 850-900 with Aldon + Lumentition. My 1380 sits around 1000. It will go lowere but I dont want to.
Dean Smith ('73 RWA)

Seth,

All 23d4's I've come into contact with (Cooper S, early 1275 midgets) and some Marina's did not have vac advance and had timing curves to suit - from the factory.

Not all HS2's self centre only later ones (this is usually refered to as needle bias), certainly up to late 1972 they did not. Required slackening off screws and retightening / checking free fall of pistons.

The early 'H' series did require the full centering procedure.

R.
richard boobier

thanks for the info guys, not been in the garage tonight, but I can add that the carbs are the original 1970 ones from the original engine, the marina engine came without any carbs you see :)
phil near bristol

update: I'm still confused, but slightly better informed :)

took the distributor out and cleaned it to find the model number, whcih is apparently:

41404H
43D4
No vacuum
1975-80 BMC
998 Mini (Canada) 1975-80, 1974 onward Leyland
(SA) 1.3 van, 1974-77 Morris Marina 1.3, 1975-78
Morris 1.3 HC

which would make sense :)

I've just been in the garage and got the car up to temp to the point where it was idling reasonably happy at about 1300 rpm - adjusting the distributor to slow it down any more made it run badly and stall.

So I turned to the carbs - first off I did the 'raise the piston' test.

the nut on the back carb is backed off 10 'flats' and raising the piston appears to make no difference to the idle, so is about right ?

but, the front carb, no matter how much the nut is backed off, from none to as far out as I dare turn it, as soon as i raise the piston, the engine immeadiatly stalls.

further info: it pops a bit on over-run, runs on a small amount when i switch off, and plug number one is very very sooty still.

any more ideas guys ? does the front carb have fueling issues ? or broken in some way ?
phil near bristol

I had a similar problem - a permanently rich mixture so sooty plugs, whatever way I adjusted the nut. Turned out the carb jet was jammed - i.e the choke was continually on regardless. Maybe see if it moves up and down as you apply and release the choke (or down and up to be precise)
Graham V

Phil not sure why you are reluctant to simply set the timing correctly but hey it is your car!

however what is intriguing me is this statement?

""adjusting the distributor to slow it down""

What do you mean? are you saying that the engine is running at 1300RPM with the idling screws backed off totally and the only way to slow the engine down is to set the ignition timing incorrectly?

If the idle is too high and the idle screws are fully out then the problem is:

Either you have an air leak around the carb/manifold or your throttles are not closing correctly?

If that is not the case then dismiss everything I have just stated. Except please set the timing up and concentrate on sorting the problem. when the timing is set then it is no longer a problem!
Robert (Bob) Midget Turbo

bob, i'm not reluctant to set the timing properly, I simply don't know how to :)

the pulley and timing cover i'm using aren't from the same engine, so I need to make my own marks.

so:

if I turn the engine to TDC on piston 1, where do I mark the pulley relative to the 'prongs' on the timing cover I have (from a midget) ?

I consulted the haynes for the marina and it says this:

http://www.spiny.org/timing.jpg

which to me, makes no sense. if the piston is at TDC how can it be 9 degrees BTDC, unless the mark on the pulley is set at 9BTDC, in which case, how do I measure my Marina pulley to make the mark in the right place ?

I'm obviously missing something quite obvious here :)


as for the idle, yes it's at about 1200-1300. I don't know if this is because of the timing, or the fueling.

cheers :)
phil near bristol

Phil,

If you had the correct timing marker and pulley groove you would simply set pulley groove to 9deg before tdc on the timing cover.

As you have differing items you need to first mark the pulley with white paint against the tdc pointer position on the cover when you have the engine at tdc.

Then rotate the engine in correct direction again until the painted pulley mark is at 9 deg btdc on the the cover.
It is then statically timed

HTH

R.
richard boobier

ok, i'll give that a go, then presumably, once thats done, I rotate the distributor until the points are about to open with the rotor arm pointing to lead 1 ? and static timing is then set ?


phil near bristol

Richard, I have a midget produced in august of 1970 that has had dual HS2's from original. They have self sentering needles.

For dynamic timing, I suggest this video
http://www.youtube.com/watch?v=hpp67aqwM2Y
S.A. Jones

Whist I do not like the method used by Richard (for the reasons stated previously) I do not want to confuse the issue anymore than it is, so do as Richard says, at least it will get the car running. Be sure however to turn the dissy CLOCKWISE when doing the points test for static timing

I like John when he says the dissy bolt is 1/4 British or 7/16 American? I assume he believes AF is American fine? surely not :) AF is "across Flats" isn't it?
Robert (Bob) Midget Turbo

Phil
Have a look in the MGB technical area on this site as there is a current thread headed "how to determine top dead centre". It may help.
Bob - I dont have a B, just being nosey!
Graham M V

I too saw that Graham (wouldn't dare comment on any MGB thread :) LOL)
Anyway I though Dennis' spark plug TDC modification was brilliantly simple and I will make one myself. Beats me messing about with a DTI through the plug hole. You can learn so many great techniques here.
Bob Turbo Midget England

Yes agreed Bob, it should give the answer in seconds. You should make a few dozen and sell them on ebay! (I can't as I don't weld)
Graham M V

This thread was discussed between 06/03/2010 and 13/03/2010

MG Midget and Sprite Technical index

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