fuel pressure befuddlement, huh Options

[r3dplanet]

Because I can't leave things alone, and maybe because I'm always trying to figure out the last 3% of why my 1971 1.7l engine doesn't purr exactly right, I spent some time with the Haynes manual to look things over.

I thought I had checked out the fuel pressure valve before, but I never really have. The book says (as do several knowledgeable D-Jet wizards) to set the pressure at 30psi. Mine is set to 35psi. Five pounds too much. Huh.

So I adjusted it back to 30psi and the car ran terrible. I thought there might be a change in timing and I was right, but even by re-timing the engine it still ran horrible. So I pushed it back to 35psi. Now it works.

Mostly.

But this raises a question. Why is it set so high? I nudged it up a little higher to 36 or so and it actually ran a tiny bit better. I don't like setting it so high, so I'm confused. The fuel pump isn't stock as far as I can tell. Or least it doesn't look at all like the one in the Haynes manual.

Any thoughts?

[orange914]

i wonder also, if the fuel pump isn't stock and doesn't produce the same volume then the higher fuel pressure may bandage fuel needs? that was a good sugestion to check at least c.o. & h.c. levels. if it ran good until the fuel was messed with, that should rule out mechanical and electrical aspects of the drivability. in other words a fuel related issue.

i've also wondered if todays fuel quality effects drivability. by raising the fuel pressure (additional fuel) it may alter drivability also?

i'm running 32 p.s.i. if for no other reason to help cooling. air cooled motors like porsche vw run cooler and better with a richer (raised c.o. level).