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MG Midget and Sprite Technical - running out of ideas

Can any one tell me why my 1275 starts to seem if its running on 2 at about 2500 rpm then it will drive through it and keep going to red line. its had plugs leads coil ive set the carb jets level then two turns down .when it starts to do what seems like its lost power if i pull the choke out it helps it to run better ive not had a good tick over for a long time but after cleaning the dizzy and re set the points it ran spot on ive cracked it so went for spin still doing it and tick over uneven .also new petrol pump fitted could it be head gasket ?any ideas will help thanks
b bithell

What is the engine specification, carbs cam etc?
David Billington

1275 no mods 1/4 twin su
b bithell

Manifold gasket?
Greybeard

>>after cleaning the dizzy and re set the points it ran spot on<<

What/how exactly did you clean the dissy?

Have you rechecked the CB points gap since you last reset it?

Have you fitted any new parts just before and during this problem?

Any misfiring?

Anything at all non-standard/away from original on the car?

Often it's best to go back to the start and cover the basics and recheck what you've already rechecked. Check/set tappets, CB points, plugs, timing and mixture in that order, if you have to adjust any item in that chain then you’ll also need to check, and adjust if required, all the items that follow it in the chain.





Nigel Atkins

Nigel no nothing away than standard only the pump its a fosit cube but it was doing the same before it was fitted .It seems to be when its hot and under load i will look at the manifold gasket. thanks for ideas.
b bithell

AND I removed the dizzy and gave it a clean with carb cleaner and set the points 15 tho tick over spot on 7000 revs when i got back tick over lumpy some one said they had the same worn dizzy bush thats why i looked at that but its ok no play in bush.
b bithell

Change the condenser for a good quality one, most are rubbish

http://www.distributordoctor.com/distributor_condensers.htm

Dominic Clancy

You've not mentioned it but the obvious culprit would be a sticking jet needle. This would explain both the tick over and misfire you're able to drive through. So I'd start by cleaning the pistons and suction chamber, and after centering the needles tweak the oil viscosities to get a synchronised and repeatable drop time. If you haven't already done so, change the needle valves for viton tipped ones, as you may be getting a little extra fuelling which is OK at high revs, but causing a problem lower down.
f pollock

Thanks Mr pollock the pistons and suction chambers are clean but i will look at the centering of the jets ive got the carbs and manifold off and wating for the gasket to come the old one not looking good so ime hoping its that. How can i tell if the jets are not centering as they fall with a thud?
b bithell

Sounds like they are centered. But push both pistons to the top (dampers installed) and check they hit the bridge together. If they do they're fine.
f pollock

Refitted manifold all new joints still the same so next thing to look for headgasket sticking valve or Spring had cup of tea went back long shot change spark plugs for some old ones bingo no misfire wheat for drive running spot on teach me to get plugs off evilbay




b bithell

Well done.

See my previous post.

NGK plugs are good, found out this week 0.028" gap is best.
Nigel Atkins

Nigel the plugs i removed were e bay n9y the ones i put in are NGK they were in the car when i got it 17 years ago ive set them at 25 tho i will try 28 if you think thats best thanks


b bithell

b,
I've had one duff Champion plug, it was NOS I got off eBay a while back before I switched to NGK.

Personally for the small cost I'd swap plugs that were in the car when you got 17 years ago especially if you don't know their age and use before you got the car.

If the car is to be more of a static display piece or even perhaps a sunny Sunday bimble conveyance then it not running at its best potential might not matter but if you want to drive it as it was designed and potentially capable of then keeping parts that work but are passed their reasonable range of efficiency isn't a good idea.

The difference in plug gap isn't tarmac tearing and will be lost if the rest of the car isn't fully serviced and reasonably well set up but I'd put in new NGK plugs and set them for 0.028" (thank you Peter and Keith).

Nice looking engine bay, you can have have it running well too.

Full servicing of the whole car will help to bring out its potential, these engines also like clean air filters and oil and filter changes as required.
Nigel Atkins

Nigel thanks for the advice I only used the old plugs to see if it would make any difference and it did I will get new plugs this week.
b bithell

Good man.

I didn't mention it before but have decide to now, if those braided fuel hoses are newish do keep an eye on them as previously (still?) there's been a lot of piss-poor quality rubber about and the braiding can hide the rubber's deterioration. If the rubber breaks down from the inside it can mess with the running of the engine.
Nigel Atkins

Thanks i will have a look at them
b bithell

This thread was discussed between 06/08/2018 and 12/08/2018

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