Carburetor heat soak permanent solution
Good evening all,
I have a Series 3 with the original 2.25 L, a Weber 34 ICH carb and an electric fuel pump. Heat soak has always been a bit of an issue but especially in recent times with more ethanol in gas. Having to crank the motor forever with your foot on the floor in front of your mates is embarrassing and irritating. I have done all the regular things to combat it: heat shields, isolating spacer, float lever adjustment, etc with no luck. I got an idea from a Volkswagen Beetle forum (they use Weber 34 ICH carbs too) which I have implemented with success and I thought I would share it here in case someone is battling the same issue.
I tapped a 1/4 fitting into my fuel bowl with a brass connector to it. I soldered up the brass pipe and drilled a 1/16 hole in it and ran a pipe back to the tank. The theory was that the fuel pump would supply way more than what I would lose through the bottom of the bowl and the engine would run just fine. The problem is that there isn't enough head from the carb to the tank to get gravity to do all the work. When the engine heats up and there is a tiny bit of backpressure in the tank, the fuel bowl won't drain and the heat soaking would persist. I then installed a second light duty fuel pump on the return line that would switch on for 10 seconds when power to the ignition goes off. This did the trick. So when I switch off the ignition, the secondary fuel pump goes on and sucks the fuel bowl (and any additional fuel that is delivered with the residual fuel pressure in the supply line) out of the carb and back to the tank. When I am ready to start up again, the main fuel pump fills the bowl up within a second or two and it starts right up, no problem.
All of this does add some complexity to a simple carb setup but I wanted a permanent fail safe solution. This works 100% of the time.
Hope this helps someone!
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