Fuel Pump Mythbuster #2

Posted by fred kanter On 2011/6/2 19:33:11

Can fuel drain back from the carburetor and leave the carb empty, making it difficult to start and necessitating an electric pump? I have read this numerous times in these forums and decided to analyze the alleged problem.

1. Fuel enters the carburetor float bowl through the needle valve. The valve is always at the top edge of the float bowl, therefore if there is any drainback it cannot empty the float bowl at all.

2. Fuel pumps have an inlet valve and an outlet valve. Both of these valves are one way only and allow fuel to flow into the pump from the tank through the inlet valve and out of the pump to the carburetor. Fuel cannot flow in the other direction, that is back from the carb and into the pump or tank.

3. There is rare exception if BOTH of the valves are leaking, but in that case the pump would have very low pressure and need replacement. What would empty would be the line form the fuel pump to the carb. An electric pump would help, but a new mechanical pump is what is needed. The bowl would stay full and the car would start.

Answer, in a word, NO.