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MG Midget and Sprite Technical - unhappy engine all of a sudden

Hi all, wondered if there might be a very simple reason and solution to a problem i have just encountered on my Mk2 1275 midget.

I had the car looked over with a fine tooth comb by a specialist about 3-4 months ago with the great result that there were a very few little things to tinker with. Ever since then she has been running like a dream and i was going use her on my wedding using wedding cars tonbridge day three weeks ago.

My brother jumped in to drive it having never done so before so i let him go round the block to make sure he was happy with it. The car started as normal, drove away lovely and all going well.

Then about 5 minutes in the car starts to suddenly struggle on acceleration, almost as if one of the cylinders has gone. However when we coast the car down a hill it sounds fine with timing spot on. On stopping at the next junction the car is now not happy really even at idle. I jumped in the driver seat and drive her back to the garage all the while the car really struggling under acceleration.

Clearly i am a novice on mechanics so is there anyone out there who has read this and knows exactly what this may be and the resolution to my problem?

Thanks all

B Priestley


it's either fuel or ignition

car was looked at - any service work done, parts or compomnents replaced ?

photo of engine bay might help

have a look in Archives

have you got a copy of the owner's Handbook, could refer you to page numbers then

what year car?
Nigel At

Sadly it is impossible to accurately determine what is wrong with your car without careful diagnosis.

Shortly you will receive here a whole host of things to check that will merely confuse the issue and if you change something you are likely to do more harm than good.

On the plus side it does not sound to me like a big problem and I would assume someone with a good bit of experience with engines will solve this problem within a few minutes of diagnosis.

By the sound of it the person who set it up a few months ago seemed to know what they were doing so why not give them an opportunity to sort it for you?
Robert (Bob) Midget Turbo

its a 72 car. in the service it had its plugs changed and a new pin in one of the carbs. I also changed the fuel pump earlier on in the year for an electronic one and had now issues with it.

I have a handbook back at home (in the office currently...)

B Priestley

ETA: typed this whilst you were posting

sorry can't help at moment (and photo too small) sorry got to go

Bob's spot on, if you look in the Archive you'll see very long threads where all kind of guesses are made

I didn't have time to type the usual but a cut and paste now

without logical step by step diagnostic the other approach is the scatter type which is to look at or for all kinds of causes and solutions every which way but this method mainly relies on luck to find the solution and can be a very time consuming and wasteful approach and can give incorrect results

you could help to speed things up for yourself and others by putting up your vechile profile and adding your first name by clicking on the Customise link at top of page (if you want to do either that is)

Mk2 1275 - could be a typo or a Mk2 with 1275 engine, doesn't matter much on this question but might on future questions

you don't have to know very much about mechanics to solve a lot some problems as I am proof

leaving it to an expert although often a good idea is not always convenient or necessary for simple things you just need to get yourself a library of information and the owners Handbook is cheap and a great source of lots of information
Nigel At

thanks very much for comments and advice
B Priestley

site's on a go slow my end now

probably best to deal with matter when you're back with car

(typo Mk3)

my first thoughts were choke, not used properly or stuck cable

BUT - that is not logical diagnostics (but easy to check)
Nigel At

"Then about 5 minutes in the car starts to suddenly struggle on acceleration, almost as if one of the cylinders has gone"

Even without your being an "expert", let's assume you do know the sound an engine makes when one of it's cylinders stops working as it should.

So, it might actually be running on 3 instead of 4.

Simple to check first. Are all the HT (spark plug leads) sitting tighly on the plugs?

Then, start the engine and let idle, if it will. Then wearing a pair of dry gloves (rubber preferably), pull each lead in turn off it's respective plug. (the gloves should prevent you getting a bit of a shock).

Does the engine note change?

If it IS running on 3, when you pull a working plug, the engine will likely stall. (stop).

If, or when, you get to the cylinder that is not firing, nothing will change. That is, it will still be running on 3 cylinders.

Then you can look to do further checks to find out why.

Beyond this, I agree with Rob, get someone who has some knowledge of machanics, or better still the specialist you used last time.

I would say that without being lucky, it is very unlikely that someone will be able to tell you exactly what's wrong on this BBS, in this particular case. There is simply not enough information to go by. Sorry.
Lawrence Slater

"I also changed the fuel pump earlier on in the year for an electronic one and had now issues with it."

Did you do this yourself or pay someone?

Have you checked the electrical connections and fuel lines? This may be running intermittently.

You see? I'm afraid it's all a bit guesswork without more to go on. And as Rob said if you start to do things that you don't fully understand you might make it more expensive to put right.

On the other hand, you can't really do much damage imo.

So if you fancy learning, buy a work shop manual and read the fault find section, --- symptoms and cause.

It's a great way to waste time at least. :)
Lawrence Slater

As others have said, it could be anything, but I have had this on other cars in damp weather, give the plugs and leads a shot of WD40 or damp start, not expensive, quick and easy to do, and cannot do any harm.

Dave Barrow

Agree... It could be anything... Vac leak, parking brake set, clogged carb jet hose, faulty fuel pump, bad gas cap, stick valve, desial fuel instead of car gas... Anything

But i love Bobs advice.... Go back to the shop you had it tuned at 3 months ago, it really sounds like they know what there doing


A 72 is a MK3 and indeed has a 1275 as said

New parts always fail!

If you use the car several times a week go back to a new SU pump
If it is an occasional car keep the electronic pump.

If you are not a hands on person keep the car as simple as possible (realy do not modify a thing)as they are the most reliable that way.

And follow Bob's advice.

But try to get a good explanation of what they have done.
And then get the handbook and a haynes.
Then start with simple maintenance to get to know your car.
Eventualy you will be able to solve these problems your self
Onno Könemann

there you go at least a dozen different possibilities given - along with good advice

anyone could be correct or all wrong

that's why you need a full and proper diagnostic appraoch preferably with just one (or two) guiding you based on the answers you give to their questions (working like a flow chart)

I was naughty as I started the flood of possibilities to prove the point of what will happen but I'm sure it would have statred anyway

oners Handbook and Haynes if you must, factory Workshop Manual is better IMO

Haynes (or facatory Workshop manual) for repair but owners Handbook for prevention

in case you're thinking of something different this is the owners Handbook (red cover Ref:0057) -

and factory Workshop Manual (Ref: 002) -
Nigel At

I must admit I rarely use the hayenes and do not know how good it is.
The mini one is fantastic so I assumed it was good as well.

I have acces to something better an MG mechanic with 40 years experiance ;)
Onno Könemann

Have you tried the car since? Is it ok when cold? If it happens when warmed up I'd suspect a condensor issue.
J White

If OK when cold and not when hot I would also check the points gap if points are still fitted. I had one set where the points heal wore rapidly and gave problems when hot but it started and ran fine when cold, turned out the points heal wore and after about 2 - 3 months the points gap was non-existent and closed up when hot. I dismissed the points as a source of the problem at the time as they were new, you live and learn.
David Billington

Sounds like one of the hoses from engine to carb came off.
Alex G Matla


The Haynes is ok in my oppinion. Yes it has some errors and omissions, but these only serve to make you think imo. It's all I have used, and cover pretty much all you need.

No doubt if i had the original BMC manual i would praise that.

What I am saying is, that any manual is better than none, and once you know the car, you won't need one anyway, apart from occasional reference.
Lawrence Slater

thanks very much for all your thoughts and ideas. I looked into it and cylinder no:3 is not firing. Turned out that the spark plug was covered in oil as the piston ring is worn. I have cleaned it up and the car is running fine again. Looks like a winter project for replacing the rings in all cylinders (and a good check over the engine seeing as it will be taken out).

Thanks again all
B Priestley

So there you go then. You were spot on when you said you thought it was running on 3. Hunches are often right.
Lawrence Slater

This thread was discussed between 05/10/2011 and 12/10/2011

MG Midget and Sprite Technical index

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