I am modifying a stock TPI fuel pressure regulator (FPR) to make it adjustable. I would like to change the spring so that it is softer. Anyone know of a good source for similar sized springs? The goal is to use the stock TPI FPR and make it be a rising rate AFPR for boost. That is, instead of the stock 1:1 rising rate I would like to intall weaker spring and make it around 4:1 (4 PSI of fuel for 1 PSI of boost). Years ago there was a webpage that showed a DIY TPI fuel pressure reg. mod.

i dont understand what your asking. to make it adjustable you dont need a smaller spring, if you drill and tap a hole in the top of th housing and put a small washer above the spring inside the housing the farther you screw in(compressing the spring) the higher the psi you will get. im not 100% on which way you screw it in but ive heard of peole putting pennys above their springs for a higher psi.