MG Car Repair: Fuel pressure, fuel pressure gauge, fuel pressure regulator

Question
I have a 1979 MGB. The electric fuel pump has been replaced with a solid state aftermarket unit. The carb is a weber downdraft. I am installing a fuel pressure regulator. What is the recommended fuel pressure for this set up?

Answer
Hi John,
I have nothing in writing that would tell me what a downdraft Weber should use for pressure but I have checked many MGBs with several different kinds of Webers and other carbs over the years and found that all performed well with a low of 1.5 PSI up to 3 PSI.(at the carb.) I have had customers purchase aftermarket pumps and they installed the pump only to have flooding problems and I often found as high as 7 or 8 PSI. I found that most MGBs can't use enough fuel to make 1.5 to 3 PSI pressure not supply enough fuel to keep the float chamber full.
The diameter of the float needle and seat hole verses the ability of the float to lever the needle closed usually determines the amount of pump pressure at the carb. I only ran into one carb with the needle and seat hole was far too small for the engine it was used on and thus fuel starvation, so rather than increase pump pressure we just located a larger orfaced needle and seat to correct the problem.

I ran into this in an MG dealership once when a customer acquired a SU pump for his MG midget and it had a problem. The pump looked correct but closed study showed he got it from a Moris Minor and the Minor pump is mounted under the hood and up high. SU had made this pump a high vacuum / low pressure pump where a Midget had the same looking pump mounted low in the rear of the car and thus a low vacuum / high pressure pump.

A balance of enough pressure to keep the float chamber full under load and yet not so high as to over power the ability of the float to close off the fuel when the chamber is full.

My opinion is to set the pressure at 1.5 PSI and put a fuel pressure gauge in a "T" and run the gauge out from under the hood and put it under a wiper arm so you can monitor the pressure under hard acceleration. Fuel starvation due to not enough fuel in the chamber will give you a hard "cut off" of the engine. Just raise the pressure to 2.5 and test again. My guess is that you will not need to go beyond 3 PSI max. Let me know.
Howard