91z28 98ta

i have just finished tpi to carb swap. im using the mallory 4309 return style regulator. Ok when the car is idling the fuel psi gauge sits at 0 then after a few seconds (im thinking after fuel is depleted from fuel bowls its shooting in pressure) the gauge will shoot up to 9 and go back to zero, so i adjusted my pressure to 8 watchin it when it shoots up. anyway is this correct is it just doing this because its at idle and doesnt need a constant stream of fuel into carb?? the mallory regulator is making a funny vibration noise when the fuel pump kicks in is this normal? im assuming its doing it when its dumping excess pressure back to tank but should there be a loud noise?? thanks for any help and advice

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mos68x

My Spectre one is doing something similar, only thing is mine doesn't feed more fuel at all. I took it off the carb with the pump running and the fuel wasn't getting past the fuel pressure regulator at all. I double checked it and with the pump off and off the carb, but turning the pump on starts putting fuel out the regulator. The one that I have only goes up to 5.5 psi though, is that going to make a difference?

91z28 98ta

ive always heard that 7 to 8 psi was the best pressure for carb setup, but i have 750 on 383 stroker a smaller carb may require less psi not sure.

five7kid

Holley says 4-7 psi. Edelbrock says optimum is 5.5 psi, no more than 6.0 psi.

Pressure isn't dependent upon the size of the carb. All pressure does is make sure fuel gets into the float bowl. The fuel is not under pressure in the fuel bowl (other than atmospheric), it's basically a pool of fuel out of which the carb draws to mix into the air stream going into the engine.

The fuel pump should be capable of maintaining pressure at all times, meaning from the time the pump is turned on with an empty bowl to the time the bowl is full and the float closes the needle/seat.

First I'd check to make sure you have the inlet, outlet, and return hooked up properly. If you used the vacuum port on the regulator, don't - it's for boosted applications, not NA.

If those things are correct, then you either have a bad pump or a bad regulator.