Running hi octane fuel in an engine that doesn't need it, will make the engine run slower. Higher compression like 10:1 will need a 50/50 mix of 94 and 89. If you have 9:1 by all means stick to 87-89 octane. Make sure it starts easily then knock is back a few degrees. Next, set the initial some were between 18 to 22. Next, remove the vacuum advance and screw down the points plate. I would mark the 30 degree before top dead center on the damper. I was amazed at how much more power the 421 made after doing this. The first time I tried this was on a 64 Bonneville 421 one Carter AFB. It should remove any fuel percolating issues. So the fuel pump is constantly moving fuel. Put a 3/8' tee at the fuel pump supply port. You should be running a 1/4' return line. I don’t think the excess pressure will hurt the carb… New carb should be on later today, so curious to see if the mileage is still atrocious. So too low with a regulator, and too high without it. I was in Autozone earlier and they had a pressure regulator in stock, but it said adjustable between 1–4 psi. Could the excess pressure contribute to the suck gas mileage? Maybe blow past the float needle? I’m surprised my stock mechanical pump is pushing that much pressure. Edlebrock recommends 6psi max and suggests 5.5. So other than being over carbureted, I also see my in-line fuel pressure gauge is bouncing floating around 8-10 psi at idle. Odd thing is it seemed to run pretty good, but the gas gauge was in a death dive. So the new motor (350cui, 300 hp, GM crate engine), with less than 70 miles on it, is until today, running an Edlebrock 750, (transferred from the old engine). It was not awful, it was holy crap awful. Prior to pulling it apart, I topped off the tank and crunched the numbers, suspecting my mileage was pretty awful. Oh, BTW… I would never dog the S- out of my car. Been reading up on them…which also takes time. Definitely interested in installing an air/fuel gauge later. Got it up to 13-14 with idle air adjustment before mama rang the dinner bell. re-tuned the new carb with a vacuum gauge but didn’t have the timing light on it. Pulled a couple plugs and indeed it’s running rich. I’ll install a secondary gauge for verification. In that light, I’m starting from scratch, hopefully with my head out of my excretion orifice. Also, until there is something to report, I’ll shut up.Īs I wait for the regulator to arrive, I came to the conclusion, I’ve been distracted and kind of fixated on the high pressure issue. I haven’t posted much on corrective actions, because I can’t tinker on it 24-7, and racking up miles for comparison takes a little time.

Delco vacuum pump in big cam 350