Still running rich, and Im trying to narrow it down. This might be a dumb question, but if there was something that was blocking my return line from flowing 100%, would that cause fuel pressure to go up? This is going on the idea I have of what causes the fuel pressure - resistance from the spring to get into the return line? Maybe that is incorrect.

Thanks for any help.

 

yes, if the return line is blocked FP can go up. the regulater lets as much fuel pass through, as it needs to maintane the correct pressure upstream. if that fuel cannot freely return, it can back up, so the regulator cannot pass the needed fuel, thus raising presure.