MG/SU carb Problem

[tractorjames]

Hi, sorry its not stag related...

I have a mate with a MG BGT which has a misfire issue.

The car will run perfect for approximately 30 minutes till it gets hot then when the throttle is pressed it will miss badly, at constant revs and throttle it will still run fine until you ask the engine to accelerate. This gets slowly worse sometimes resulting in total cutting out of the engine. Leave it to cool and it will start and run fine for another 20 minutes or so.

We have worked through everything basic, and tried new parts such as coil, lunenition module, fuel pump, fuel lines, filter, distributor cap etc and the only two things we haven't looked at are the carbs and the distributor its self.

Upon removal of the carbs we found that one float was 1mm proud of the float chamber face and one was 3-4mm proud whereas the should really be 1mm (+/-0.5mm) recessed from the face.

My first question is would this huge difference cause the symptoms above?

Also is there anything in particular to look at in there that may be causing the problems?

Any thoughts at all would be much appreciated.

James

[GDPR]

Possibly, assuming the carbs are HIF.

Renew the needle and seats, set the floats to 1mm, then wind the jets up until they are flush with the bridge.
Make sure the shoulder on the main needle is flush with the bottom of the piston and adjust if not by slackening the screw in the side of the piston and giving it a tug.
Screw the jets in one and a half turns and assemble - should give you a decent startup setting.

If the heat shield between the carbs and manifold is missing it can create all manner of issues. While you are at it the manifold to head nuts are always coming loose so give them a tweak....

[wilf]

Is there a separate rev limiter fitted?

[Bandit1200]

Fit a red rotor arm.
Tired rotor arms have been known to cause problems.

[73stagman]

Is it the right coil for the electronic ignition? Ballast and non ballast discussion again! Symptoms are the same as the coil breaking down when its too hot.

[Another Peter]

I'm with Neil.

Faulty/incorrect coil. Don't think that because it is new that it is performing well. The standard of manufacture of some new coils is rubbish, as are rotor arms. (so perhaps I'm with Bandit1200)

[staginhiding]

Just fitted an Accuspark kit,to a 1968 MGB inc coil, leads,cap etc..it transformed the car and eliminated all that side of things..

[judderman]

Hi James

Are the heat shields fitted between the exhaust manifold and carbs mgs suffer from fuel evaporation when hot I had the similar problem
cheers Ian

[tractorjames]

Thanks for all the advice, to answer a few q's

Yes the carbs are HIF's

No rev limiter

Will have to look into the coil although the one fitted was put on by a reputable local garage (means nothing I know!)

Will look into a new rotor arm although the one in it looks perfect.

Yea the heat shield is present but tatty, may be worth temporarily beefing it up to see if it makes any difference.

One thing I have noticed the under bonnet temperature of those MG's is frighteningly hot - maybe a problem???

Thanks for all the thoughts,
James