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MG Midget and Sprite Technical - New to Midgeting

Hi I am Net to midgets although I have owned a Triumph Stag in the past.
I am on a steep learning curve, although most of the bit on the Midget are fairly simple. One thing that is bugging me at the moment is the fact the car wont run on choke then when it is finally warmed up revvs its nut off on tickover. Mybee its something to do with the pancake filters and carbs not set up properly. I am going to check the needles on the carbs to see if the correct ones are fitted for the type of air filters fitted. Any ideas ?
S Langston

no idea what the problem is, but welcome, someone will no doubt be along with some ideas in a moment!

Malcolm
M Le Chevalier

Will not be the needles but you need to check on the throttle disks closing correctly in the carbs or an air leak. For the car to rev it requires air to get into the engine and not excess fuel.
Robert (Bob) Midget Turbo

Welcome

Bob will help you with your problem I'll do what I normally do and suggest you, if you want to, show your car's profile to help with answering question

and my usual advice to new or potential owners as it's about the only thing I usually get right

My advice to new owners -

buy a owners Handbook as it tells you so much you need to know as to own, drive, service and maintain your car - http://www.mgocshop.co.uk/catalog/Online_Catalogue_Handbooks_5.html

Always have the battery in good condition and all battery connections and leads clean, secure and protected, same for all electrical wiring and connections

As soon as possible do a full and proper 36,000 miles service only miss out items that you have 100% proof have already been done very recently, including;
g/box and back axle oils
brake and clutch fluids
coolant
dissy cap, rotor arm and leads (buy good quality ones)
http://www.distributordoctor.com/rotor_arms.html
fan belt

Check the age of your tyres if they are 6 years old or more replace ASAP regardless of tread depth, this will improve, the braking, steering, ride, handling and possibly noise, of the car greatly

Use the car regularly - to get used to it, sort out any wrinkles and prevent others, and enjoy it

Every few weeks check your horn and wipers work (no problem if you use the car regularly)

Follow regular checks, servicing and maintenance as per owners Handbook

Drive in all weathers, the Midget hood should be very watertight if fitted correctly and the heater is more than adequate, if working correctly, for the small cabin

Do not do any cosmetic or improvement work for at least 12 months of regular use, unless you need to replace parts or components, as you may need to use the money elsewhere on the car

Also very useful, you can get suppliers catalogues for free to get you started to see where things go but in my personal opinion theyíre not as good paper copy like - http://www.mgocshop.co.uk/catalog/Online_Catalogue_Parts_Lists_3.html

Cheers, enjoy your car
Nigel Atkins

or it could be a vacuum leak, easy to happen if the distributor connection is disconnected, or if the vapor recovery system is messed up / hose is cracked

less likely, but quite possible also is a leak where the manifold meets the head


Norm
Norm Kerr

S - could you explain more what you mean - when you say it won't run on choke - what exactly does it do?

LOL - it's ruddy hard to tell anything on 'tinternet! Plus, which engine is it - what carbs are you running - etc etc etc etc ... :P

I'm sure that, if you've managed the Stag, then a Midget is perfectly simple for you - don't suppose you've still got any parts from it?????
rachmacb

When the engine is cold and i start it it will only run without choke then cut out. If i pull the choke cable out it kills the engine imediatelly, this happens wether the engine is hot or cold. When it is warm it idles at about 1500rpm. I have been told by someone that i may need to change the needles because of the pancake air filters fitted to the car. Currently it has ABT needles fitted in to the SU AUD665's. I have bee thinking about fitting AAQ needles to see if they match the filters better. It is the 1500 engine. I dont know if it has any other enhancements as it all looks standard, apart from the filters of course. The exhaust is a standard looking two box part.
I am going to give the engine a good service this weekend. Also i will replace the ignition leads. The cap and rotor arm look ok.Oh just thought it has a modern type of electronic ignition an ignitor type thing.
As soon as i can sort this out i can start enjoying the Midget more !
ps. Would it be better with the original type air filter box fitted ?
S Langston

S don't dispair it will work out and you'll get help but please read this fully for now

I know you want to get this problem out of the way but I'd say start with basics

Service the whole car not just the engine - at the moment the car wont get you into too much trouble as the engine don't run - but when it does it's one of the less important items after brakes, steering, tyres, suspension, ect.

To see if these pancake filters (do you mean wiremesh type or K&N? photos would be good if possible) make any differene remove them

Persumably it ran before with the present needles so don't think about changing them yet

Faulty rotor arms and caps often look good

Electronic igniter could throw up a fault - but let someone take you through a step by step diagnostics of the problem otherwise you'll get the scatter gun of suggestions of this, that and the other like I just did with naming the electronic igbiter without any structured reasoning

I know you want to deal with this problem but reread my previous post, get the owners Handbook, do the full and proper 3 year service - best tuning you can do

Thinking about changing the needles before full and proper servicing is the wrong way round
Nigel Atkins

>>. If i pull the choke cable out it kills the engine imediatelly, this happens wether the engine is hot or cold


It's rare that pulling the choke out kills an engine, since the first part of the cable movement increases the idle speed (or should do) and further choke cable pull richens the mixture (or should do!).

Both increasing idle speed and richening mixture normally 'help' an engine.

When the engine is running, and before you pull the choke cable out, is the engine running rich (e.g. exhaust is black, smells of fuel)?

Can you drive the car on the road?

How long have you had the car?

When did these symptoms start? What have you done to the car since it last ran OK?

Anthony
Anthony Cutler

If you are new to the car I wouldn't start changing fixed components like the needles. They are unlikely to be seriously wrong as presumably it was running OK at some stage. It is more likely a setting that is wrong, or something incorrectly assembled.

From your description, I would suspect that it is running very rich to start with, pulling the choke out is just flooding the engine completely. Check that the air filter pancakes are not on upside-down and blocking the air by-pass holes to the carbs. An easy mistake, easily fixed! And check that the needle settings are at least approximately right. A PO may have just thought that you do the jet nut up tight! The approximate start point is 2 turns down (12 flats)

Guy
Guy

If you can cold start without choke it must be very rich - I agree with Guy. It should be impossible to start from cold without the choke. Take out a couple of spark plugs - I bet they are black.
Mike Howlett

Please can someone tell me how a car revs too high because it is running rich?
It maybe running rich but the reason why the engine is revving high at idle is because either the throttle disks are not sitting closed for whatever reason or there is a vacuum leak on the carb/manifold!
Bob Turbo Midget England

True Bob,
The 1500 has an odd arrangement on the throttle cable where the lever stops by contacting the heat shield. Perhaps the cable is not fitted or seated properly, preventing it from closing. And a rich choke setting might have been set to compensate for the non-closing butterfly, in order to get a rich enough mixture to get it to start.
Guy

ABT is ok - are they K&Ns? The shape won't make much difference.

It sounds like the choke cable might be staying out - check that your spring is there and not broken - happens sometimes!

As for the rev thing - well, I dunno - I do know that Bob had to apologise for making mine rev more than I could set it to last year ;) However, that was on a set of carbs which had an air leak and there were a few other problems - however, does kind of demonstrate that the only person who knows our car is ourself!

The odd car around doesn't actually need a choke, so, it is possible that, having made all the checks and servicing it - it might be one of them - as I said, each car is it's own personality, and it sometimes just takes awhile to get used to it. My 1500, for example, if I don't put the choke in by the same stage everytime, will throw a wobbly fit and sulk!
rachmacb

Thanks for the answers. I am on that steep learning curve at the moment, the one we all ride in the first week of ownership. Everyone here has been very informative.
I am going to have a marathon servicing on the Midget at the weekend (weather permitting) I just cant understand how the choke kills the engine, so perhaps it will be something else. Is it best to blank off the emission control stuff ? (the pipes from the rocker cover to the carbs)
Keep the information coming please, it is all sinking in slowly.
Cheers Simon.
S Langston

Simon get the owners Handbook (not just for the full and proper servicing schedule it tells you loads more that you'll find very useful as an owner)

Go through the full three year service schedule

I know I'm labouring the point but when you get the Handbook and do the full and proper 36k-service you'll see why I'm labouring both

And it is highly possible that by doing both you will discover the cause of your problem (but not guaranteed)

After doing both if you've not found the cause then this will be a very good starting point for logical, progressive diagnostics, plus you'll know more about your car and be able to follow and respond to the diagnostics easier

I have next to no knowledge and aptitude of mechanics but having run classics as dailies for 20 years so Iíve learnt that covering the basics solves and prevents very many problems on the car so thatís the place to start

Cleaning and lubricating as part of servicing will help no end
Nigel Atkins

Simon - I'm sure that you already know this article, but, it's way way way more useful than most of the stuff found on here as it actually deals with the particular engine - and what you can (and can't!) do with it!

You're more than capable of doing standard services, so this will give you some ideas of what you can do next ;)http://www.totallytriumph.net/spitfire/engine_building.shtml
rachmacb

Sorry Rach I didn't know you knew Simon and his car capabilities

The 1500 Handbook will deal with the whole car including the 1500 engine and my other advice covers A-series and Triumph engined cars

Certainly the 1500 Midgets have a few more bits and bobs, sometimes rubber bumpers, and a different engine but the basics are the same

Simon's new to the car and appeared not to know a great deal about it by his posts so I stick to my advice

Certainly once he's done the basics and solved this and other wrinkles he'll find by using the car (for a good 12 months in my opinion) then he can move on
Nigel Atkins

Hi. Thanks again for the answers. Nigel i take heed of your comments and yes it is very sensible to do a full service on a vehicle with no recorded history. Also it helps with familiarising yourself with it. I am going to change all the oils, service the engine and brakes and get to know the Midget intimately.
I want to enjoy this vehicle but ulyimatelly know it is safe and reliable.
I only collected it last Saturday and drove it sixty miles back home. It drives lovely apart from aformentioned high speed idling.
It was an ebay purchase and has at sometime been extremely well loved but is now slightly neglected.
I am looking forwrd to bringing it back to life. I am lucky because it has had extensive welding repairs to the sills and floor sections with new metal welded in.
As for me i am quite a competent home mechanic and am not afraid to tackle any job thrown at me by this little car.
The thing I dont know much about is SU carbs ! Give me a Solex i will strip it blindfolded .
I have a couple of manuals, a haynes came with the car with some parts catalogues and i have obtained a factory book, so i can consult with these. Sometimes it is good to talk to others on this such forum who enjoy the marque to share tech stuff and stories of daring do.
S Langston

Don't - I just read his first post - as that sometimes gets forgotten about in the keen-ness to help!!!!

SU Carbs Simon are actually not that difficult - it's just that people seem keen to make it such! There are plenty of manuals on it though, so I don't intend to teach anyone to suck eggs, that they are perfectly able to do themselves ;)

Sounds like a typical ebay purchase - but, at least the bodywork is sorted and, if this is the only problem you've got then great - have a wonderful summer of driving - and don't forget to come to Midget50 (www.midget50.com)!
rachmacb

I am thinking about going to Midget 50. I believe that there are no tickets for sale on the day, to stop queues on the road. Trouble with Sunday events is I have to work Sundays so it spoils the day by having to leave early ! :-(
S Langston

Simon email the cttee via the website
rachmacb

Sorry Simon you know a lot more about cars than me

As rach says plenty of info on SUs

You probably know they come under Burlen Fuel Systems - http://www.sucarb.co.uk/CompanyProfile.aspx

Loads of info and diagrapms on the internet

Haynes is good(ish) for repairs and a useful companion to - the owners Handbook, which is much more informative for ownership and use of your car :)

If you can get your vehicle profile to display publicly (mine does but for someone else it didn't work) it will confirm your model of Midget and save you from putting it everytime

and if you're able to post photos it will help with explaining and confirm stuff (good photo worth a thousand words and all that)

I'm on my fourth year after buying 'a restored' car and by another 12 months it should be as near finished as I want, subject to replacing some of the parts I previously replaced of course

good luck, enjoy, keep the correct ratio of driving to working on
Nigel Atkins

For what its worth... you have the correct needle for that carb

SU AUD665's .... ABT = (CUD 1041) FOR THE 1500, the front jet is AUD 9050 and the rear jet is AUD 9051 both with a Jet size of (.09") front is black capped the rear is white capped

Needle AAQ = (CUD 1014) is for a single HS4 on a Morris mania 1.3 1275 1971-72 cars (AUD 354) and on the 1976 automatic Morris mania 1.3 1275 (AUD 436) has a jet of AUD 9450 which has a jet size of (.09")



SO IN A NUT SHELL....


(CUD 1041 (ABT)) is for a duel HS4 on a 1500. (The correct set UP)

And the (CUD 1014 (AAQ)) is for a single HS4 on a 1275 ....

Yet both running on a small (.09") Jet....

Well this should be fun to say the least to wrap the ol brain noodle around

To be honest... I have no clue as to what will Happen


Prop ...Oh yes, I am really that smart (worship me!!!)... hahaha.



Prop

Find a picture on the net of the HS4 and locate the idle screws and fast idle screws on your carbs.

For the choke problems, your fast idle screws will probably be too far out (when I got my 1500, they were all the way out, the DPO claimed I was 'choking up' the engine...but SU carbs don't really work that way...).

Set the choke knob so it's just before it actually moves the jets any amount (an extra person operating the knob while you watch the jets will make this very easy!) then wind in your fast idle screws till they contact the cams and then about 1-2 full turns more. Do each side progressively and evenly. Then (on a stone cold engine) try starting it under choke and it should work as it should. You can then fine tune the fast idle to about 1100-1200 RPM.

When it's warmed up, back the idle screws off by even armounts side by side (say, 1/4 turn then swap sides). Do this untill your idle is desirable (about 850-900 is usually good for a smooth idle, lower requires a well tuned engine, which yours doesn't sound like!)

All the above is way easier for visibility/access with the air cleaner assembly removed.

Hope that helps!
RoadWarrior

I have had a go this afternoon at getting the engine running nice from cold. I have changed the plugs and leads, set the timing and adjusted the carbs. What i have noticed though is the jets on the carbs. Following on from Prop's message, both the jets on mine are red capped (i presume the cap is the colour you can see under each carb by the adjuster nuts)
On the Burlen web site is lists the AUD665's as having an AUD9451 black cap on the front carb and an AUD9450 red cap on the rear carb.
Perhaps i have the wrong jets fitted in mine, so causing these problems.
Like i said i had a go today and got it running ok but not as good as i would have liked idle at hot was still a bit unsteady and sometimes dropped off slowly until it stalled. I think there is probably some fine tuning to do.
S Langston

well

I (Used) to have a chart of what the various color sleves and capps represented...But it appears to be hidding at the moment

I did find that the red caps did run the range of jet sizes.

sorry about that

Prop
Prop

This thread was discussed between 29/03/2011 and 01/04/2011

MG Midget and Sprite Technical index

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