MG Car Repair: MGBs engine stops running, mgb gt, living in belgium

Question
Hello Barrie,

I'm living in Belgium and actually restoring a MGB GT 1971. The car is almost ready and I am currently busy with tuning the carbs. I am facing an issue that I expect to be caused by the carbs themselves. To summarize :
When I start the engine while it is cold, it runs OK. The mixture still needs to be fine tuned, but that's currently enough to drive. Unfortunately, the engine stops by itself after running for 3 to 4 minutes only. To explain how it behaves when it stops : imagine that someone suddenly cuts all the ignition wires while your engine runs. It will simply stops .... The only way to restart the engine is by pulling out the choke to the max, and in this case pressing the accelerator strangles the engine. By leaving the car for 1 hour or 2, the engine is back alive for again 3 to 4 minutes.
Configuration : Carbs are restored with repair kit, cylinder head 18V with valves height adjusted, fuel pump and fuel lines are new, I have nice sparks on all 4 spark plugs.
Do you have any ideas because I'm stuck?
Thanks a lot for your help.
Christophe

Answer
Hi Christophe

I have been asked about this problem a few times recently.

I guess you are using E10 fuel, which is causing a lot of trouble.

As winter approaches, the air becomes more humid.  The Ethanol in the vaporized fuel is turning back to liquid as it emerges from the jets of the carbs.  As it does so, it refrigerates any moisture in the air, forming ice which partially or completely blocks the carb jets.  When you pull the choke, you make the jet larger so this allows you to limp home.  This problem is well known in aircraft, where it is called `icing up' of the fuel system, and it can happen at any temperature up to 20 degrees C.  

Somehow you need to get more heat to the carb bodies, but you must avoid getting excess heat to the carb float chambers and fuel lines.  It is a real problem.  As a quick fix, try using fuel which has less Ethanol in it.  In the UK that means buying 99 octane instead of 95 octane.  Also, if you have plastic spacers between the carbs and the inlet manifold, it might solve your problem if you replaced them with metal spacers which will conduct more heat.  The good news is that the problem only happens when starting up a cold engine.  Once warmed up, the problem should go away.   

Please let me know how you get on.  I am researching this problem at the moment and I need to know what is happening out there.