[Texasdoc]

Doing some study after work. Not looking forward to the 14 hour day tomorrow...

Anyway, I have the MSD Mallory 110gph fuel pump. I read thru the instructions and found that it has an internal bypass of 7psi. The instructions don't say how to adjust the internal bypass, even though there is an external nut and allen screw.

Continuing my search, I found that the Mallory bypass regulators include a plug that disables the internal bypass on the Mallory fuel pump. You have to buy the Mallory pressure regulator to get this fuel pump plug. I bought the Holley HP billet regulator. The instructions for their *regulator* say that the 110 unit was designed for use without a pressure regulator - it doesn't say this in the pump instructions!

What I think is happening with the fuel pressure is that the pump's bypass, set at 7, is not letting the pump put out enough pressure to push the fuel thru the lines, thru the Holley pressure regulator, up to the gauge/bowls. By the time the fuel gets up to the carb, it is less than the 7 the pump is putting out. I have the Holley set on 6.5 (per Quick Fuel's recommendation). My guess is the pressure at the Holley regulator is dropping at WOT since the pressure decreases due to friction/flow while the pump is only putting out 7. In essence the two pressure regulators are fighting each other.

No where does MSD/Mallory list how the internal bypass works. There is a spring that I am supposed to remove and replace with a plug. It doesn't list the size of the plug. Does the fuel run thru the spring and if you take it out and install a plug, the fuel cannot take the bypass circuit? OR, does the spring hold the bypass plunger in to a certain depth and putting in a plug prevents this from collapsing under pressure??? How big is this "plug" that I need? Will adjusting the current allen screw in 1/2 - 1 turns increase my pump output pressure enough so the fuel pressure at the Holley regulator doesn't drop below its set point?

Any thoughts?