Posted by Matt Wilson on Thursday, September 12, 2002 at 1:34PM :
I know this topic has come up quite a few times, but I've got yet another question about it.
I've been driving my '49 flatfender for a couple of weeks now, after rebuilding the engine. I have a brand new NAPA mechanical fuel pump installed, and I also have a brand new NAPA electric pump installed at the tank. I converted the truck to 12 volts, so the electric pump is, of course, 12 volts. At first, the truck ran fine on just the mechanical pump, and occasionally I would push a button to turn on the electric pump when needed for overcoming vapor lock. Then I would shut off the electric pump and run on the mechanical one alone.
This worked well for the first few days, but then one day the mechanical pump stopped working and I've had to run on the electric one alone ever since. I have an inline pressure gage between the mechanical pump and the carb. With the mechanical pump working alone, the gage used to read 5 psi all the time, but now it reads 1 psi, and the engine will not run unless I turn on the electric pump. When I activate the electric pump, the gage reads 5 psi all the time, so I don't believe this is over too much pressure. If I remember correctly, the manual calls for fuel pressure to be 4-6 psi.
Anyway, can the use of an electric pump can cause a mechanical pump to go bad?
Also, for those of you who use electric pumps, do you use a pressure regulator, and if so, what pressure do you have the regulator set to?
By the way, I know that a mechanical pump going bad can dump fuel into the oil pan, but I've been keeping a close eye on it and I've seen no evidence of gas in the oil.
Another related question is: Last week my truck died on the road because the carb flooded. I could smell the fuel pretty easily. I shut off the electric pump and pushed the gas pedal all the way to the floor, and after a couple of minutes I was able to restart. I've driven the truck 4 times since then, for several miles each and not had any more problems. At 5 psi, I don't think the electric pump could have pushed the carb's float needle off of its seat, but perhaps I had a piece of crud holding it open. Any thoughts on this?
Sorry for the long post.
Thanks,
Matt
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