Ok I just got some goodies for my 76 F-250 4x4 with a 390/C-6. I ordered a Preformer 390 intake, and a Holly fuel pressure regulator because I was told that a Edelbrock 600cfm carb (model 1405) should only have 6psi max of fuel pressure running to it. My question is, will I damage the diaphram OEM style manual fuel pump if I install and set this fuel pressure regulator at 6-7 psi, or will this be ok to use? Also what does the stock fuel pump put out? I was told it can produce as much at 12psi which will not allow the Edelbrock carb to function properly and could even damage it. I don't want to burn up this pump just because I was given some bad info.

Thank you,
Brad

 

The stock diaphram pump will probably be ok. Usually there is a rubber diaphram that put the pressure on the output side. If the output is blocked (read needle assembly on carb is closed) the diaphram will stay inflated with fuel and hold it with pressure. The mechanical connection from the diapram is solid on pulling the diapram (read the intake cycle) but allowed to freewheel on the exhaust side. In other words, the lever sticking out of the pump that is actuated by the cam, only pulls on the diaprham, it doesn't push.

It is much harder on these style pumps to block the intake (cause it to pull against suction) than to block the output. This is because if the intake is blocked, the diapram cannot inflate, but the lever forces it to move. This stretches and can tear the diaprham and cause it to fail.

 

As far as I can tell, this fuel pump is either OEM, or OEM replacement. So from the last post, it kinda suggests that I will be ok with the pressure regulator in-line right?

 

You should be fine.