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MG MGA - Car won't run when warmed up


I have a 1500 A that I have recently spent a lot of time re-tuning. I rebuilt the cards (twice) before I got everything running smoothly with no sticking, leaking , chokes working and good performance. She still wasnt brilliant, so I replaced the points and condenser with Electronic ignition (small internal to distributor). The car now runs and drives like dream, apart from one frustrating point. After about 30 minutes of running she wont pull unless you change down and if I then stop at traffic lights she struggles to keep running, the only way is to keep revving her. If the engine stops she will not start again until she has cooled down. She will just about start if you tickle the throttle a lot, but she wont run.

I suspect that there is something wrong with the carbs as she was doing this before I installed that Electronic ignition, could it be that the mixture is to lean and vaporising when hot? Last weekend was not what you would call a hot day in the UK so I am now at a loss

Garreth (UK)
G T Smith


You will lots of advice of things to check, both fuel and electrics. It may be worth your while telling us first your configuration. i.e. carbs, needles, filter canisters, filters, distributor type, timing, cooling (what the gauge normally shows). etc.

Your problem could be a collection of minor 'faults' or may be just one specific issue. The more you can tell us, the more likely we will get to the problem sooner.

Steve Gyles

Do you have the carb heat shield installed?
Ray Ammeter

Did you change the coil when you fitted the electronic ignition?
Malcolm Asquith

As Malcolm suggests, it sure sounds like a failing coil...very typical...If you did not change the coil, be sure and get the one that matches your new ignition.
Edward Wesson 60MGA

Change the coil first as it is an easy fix.

However, my favorite culprit would be a partially blocked fuel line or fuel filter, probably something that is floating around in the system and gets pushed over the filter or pipe outlet by the fuel flow.

Then when you switch the pump off, that piece of debris drops down out of the way and lets the fuel flow again.

You can easily check this by disconnecting the fuel pipe at the carbs and measuring how much fuel is being pumped through. I pint per minute is a reasonable flow.

Usually, if fuel flow is causing a misfire problem, the front carb runs out of fuel first. So if you take the top off the front carbs float chamber and it is empty (or nearly empty, this would prove it was a fuel flow problem.

best of luck

Colyn Firth

Some cheap and easy checks
1. Coil as above, but not as cheap and quick as ...
2. Junk in the float chambers getting under the needle valve. Causes fuel to be pumped out of the overflow and into the carb - gives very rich uneven running on one carb and petrol spraying on the exhaust pipe. You will see rust and stuff in the bottom of the float chambers. Don't know how it gets through the strainers, but it does. Clean the tank, lines, pump strainer, float chamber strainers.
3. Petrol pump stops, causing increasingly weak and asymmetric mixture in the carbs - very rough running, then engine stops. Switch off ignition, then on again and listen for the sound of the pump ticking to refill the float chambers. Clean and re-adjust the points in the pump.
D Brown


Thank you for your replies. I will check fuel components, but I suspect that Malcolm may be correct. I will see if I have a spare to swap out...

I will update after investigation.
G T Smith

This thread was discussed between 18/11/2013 and 19/11/2013

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