Re: Fuel Pump Pressure??

Posted by Rusty O\'Toole On 2009/3/20 5:25:08

Your fuel pump seems to be working normally. I believe there is another issue here, namely a slightly weak needle valve.

If the needle valve is not sealing quite tight it will not cause any problem in normal driving. But what if you stop the engine and there is pressure in the fuel pump? Fuel will slowly run into the carburetor until the float bowl overflows.

Because the jets and fuel passages start from the bottom of the carburetor, this starts a siphon action that siphons all the fuel out of the float bowl and down the carb throat.

Then, the float bowl is dry when you go to start the engine.

To me this accounts for the common problem of hard starting on old cars that have sat for a while.

If I am correct a new needle and seat will cure the problem. If no other changes are made to the carb, this can be done in half an hour.

Can any carburetor experts confirm this hypothesis?