[say10tatoo]

I just installed a new holley fuel pump in my Mustang with a 289 and a edelbrock 650 cfm 4 barrel carb. when I get on the gas the engine is back firing through the exhaust. Is the fuel pump not providing enough fuel or to little.....? It only does this when I get on it hard.....

[bracketeer]

Electric or mechanical?
blue or red?

[say10tatoo]

It is a Holley Red electric fuel pump. According to the instructions it puts out 97 gph (free flow) 67 @ 5 psi. It is preset @ 7psi. It says a pressure regulator is not required.

[say10tatoo]

got a pic

[Matts99Sierra]

put a fuel pressure gauge on it. the fuel pressure should be at 5psi. at the carb at full throttle. if the pump is preset then you might have to get a new pump.

[Old School Nut]

technically its NOT a backfire, but a afterfire.

as for your question, typically to lean a fuel air mix will cause a backfire, to rich, an afterfire, did you touch anything else???

-Leo-

[bracketeer]

I have never used a blue pump but am familiar with the reds. If they are the same other than the regulator. I know your problem.

The red electric pumps have no suction. They have to be installed below the tank and gravity fed. It seems you have the pump in the trunk above the tank. It is unable to keep up to the demand at higher rpm.

Install the pump below the tank. I built a bracket under my trunk for the pump and filter. See attached pic.

PS: That rubber line will not pass safety at the race track. Max of 12" in the entire system from tank to carb.

[say10tatoo]

I believe you are right about the pump placement. I will move the pump under the tank tomorrow. I will also eliminate the excess rubber lines....thanks for all the advise ...