Question Thanks Barrie for your help so fab.
I no longer have the mechanical fuel pump mounted on the side of engine, I put an electric one on last Spring and it has worked great.
This problem didn't start until last week, ran great through the heat of summer , as soon as the weather turned cooler it started, I thought vapor lock happened during hotter weather ?
As soon as the engine cuts off, like its out of fuel, it will fire right back up, if I pull the choke all the way out it will keep running, could something be stopped up , it kind of acts like a stopped up fuel filter that stop and unstops
Thanks
AnswerHi Steve
I think you have stage 1 of the complex problem with modern fuel. (I thought you had stage 2).
With the cooler weather the air is more humid. Once the air temperature drops below 20 C this problem can occur. 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.
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. (That is when problem stage 2 starts to happen).
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.
