Does anyone know of an adjustable FP Regulator that will work on a 502 mpi (non-cool fuel)? I did some mods to mine to make around 500 hp & the guy who reprogrammed the ECUs suggested I install the CP Performance add-on caps to the regulators to make them adjustable. Basically they're junk- they move from about 20 psi to 50 in about 1/2 a turn and don't seem to maintain the same pressure over time.

you will be miles ahead by eleminating the VST, remove and block off the stock diaphram pump, install and Aeromotive A1000 with its counter part PF regulator, modify the fuel lines as required.

I use those, they work great. Might want to check it. Or could be leaking around the threads.

Mine was very eratic when I installed it several years ago, so I bought a new Merc regulator and modified for the adjustable cap and it is steady and has worked good since.