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?

[ArtechnikA]

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.

What is your actual air-fuel ratio? or idle CO?

What first somes to mind is that you may have crud in the injectors and the increased pressure is compensating for restrictions and crappy spray pattern.

If you are actually running no richer than spec, it's probably something like that. If you're actually running richer than spec, you may have to adjust to a new definition of 'normal.' Or find whatever else is keeping it from running right that someone decided to mask with richness across-the-band. TPS "accel pump" not working right is something that this could compensate for.

But define "ran better"... Idled smoother? accellerated better? improved transient response? More power? Lower emissions?