Fuel pressure fluctuation

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64physhy

64physhy

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My fuel pressure keeps changing. I set it to 6 psi, then after it runs for a while the pressure drops to about 4. When I adjust it back up 6, it stays until I shut it down and let it cool down. When I start it cold, the pressure is up to about 9. I keep messing with it, but the pressure keeps dropping whenever it's fully warmed up. Any ideas?
Pump is a black electric carter, regulator is holley, press gauge is russel.
 
This could be a long shot but I will throw it out there. I was having the same problem. I have stock fuel pump with no regulator. I do have a fuel pressure gauge there close to the carb. What it turned out to be was trash in the tank. As the engine ran and fuel sucked through the sock in the tank it would collect debris slowly shutting off fuel delivery and thus causing slow psi drop. Once the engine is shut off the debris falls away from the sock. Once the engine is started the process would start all over again. Until I installed a new tank, sending unit I have yet had that problem. I had awful lot of debris in the old tank.

Another would be vapor lock but with cooler weather I don't think that's your case but you do however live in Cali. lol
 
I just replaced the sending unit. The sock on the old one had a little bit of crap in it. I guess it could be crap in the tank. It was about 50 degrees today when I was messing with it, so I doubt it's vaporlock.
 
Just had the same problem this past season..changed the fuel pump and regulator,problem solved...
 
I'd say your regulator is sticking especially if your pressure is overshooting to 9 psi when you've set the reg to 6. Grab a new one they're cheap.
 
It may be that junk Holley regulator. I have tried several times to like them but they kept letting me down. I love there pumps but the Holley regulators suck. I finally bought a good Aeromotive and haven't had any problems
 
I had a Carter fuel pump when my problems started happening. I changed over to a stock fuel pump and it helped tremendously but still had trash in the tank. I really don't know if the Carter is toast or what but I left the stock fuel pump on.

Like the others said sounds like the regulator.
 
The pump has a little age on it, but not much. The reg is almost brand new. I was thinking probably the pump, but hoping not. Maybe I'll just replace them both at the same time.
 
64physhy said:
The pump has a little age on it, but not much. The reg is almost brand new. I was thinking probably the pump, but hoping not. Maybe I'll just replace them both at the same time.
Click to expand...

It's hard to say about a electric pump. If you ran a hose off the pump into a gas can and it is pumping the crap out of gas then I wouldn't say its the fuel pump. Unless however the pump isn't feeling any pressure when it is just dumping into a gas can.
 
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