Accelerator pump tuning

[Gunner]

Originally Posted by elmariachi

You are saying that the vacuum secondaries on this brand new carb are not opening?

I'm not sure. I could get movement - just a little - revving it in the garage with what turned out to be a third-weakest spring. Now I can get no movement, even with no spring, but that's not too uncommon for vacuum secondaries. They do need an engine under load, not just revving.

I put the weakest spring on and got the characteristic hopping stumble of too-early secondaries, so there's that much indication that they're working.

With the original spring refitted, some hard pulls (okay, semi-hard, but definitely into secondary zone) didn't move the rod index at all.

I now have the second-weakest spring, in between the one that hopped and the one that didn't move, installed and will see how it drives tomorrow.

None of this had much effect on the low-end bog, so I put the 0.031 squirters back and changed the accel cam to a more radical early curve. We'll see how that does tomorrow, too.

PS - My deleted post listed all the diagnostics I did on the vacuum pod. It's fully functional, no leaks, no binding, etc. My only question is whether it's getting the correct vacuum signal from the carb - and those passages seem to be clear.

[patrickt]

Originally Posted by Gunner

None of this had much effect on the low-end bog, so I put the 0.031 squirters back and changed the accel cam to a more radical early curve. We'll see how that does tomorrow, too.

You might want to start letting in to your mind that the low end bog is not being caused by the carb or the ignition or the timing, but rather is a function of the cam choice for that particular engine. If you replace the carb, the distributor, the plugs, and the wires, and still have the same low end bog, then it's the cam. As much as you like to monkey with your engine, if you do change out your cam you really should go solid.

[Gunner]

Originally Posted by patrickt

If you do change out your cam you really should go solid.

But... but... would it still be REAL?

It's pretty subtle and as much as I've listed here, I haven't done a really comprehensive attack on the tuning. It's been a bit here, a tweak there as I have time and ability to tweak and test. Too many other things drawing at my time. Now that I have all the tuning pieces in hand, I should be able to take one or two big swings at it this week.

Getting the secondaries to come in properly is a first step. *sigh* I do NOT want to go to mechanicals...

[patrickt]

Originally Posted by Gunner

Getting the secondaries to come in properly is a first step. *sigh* I do NOT want to go to mechanicals...

I have a vac secondary. When properly adjusted they are superior to mechanicals -- I'm sure I'll get some flames on that, but it's absolutely true. You know you can check your secondaries with a can of compressed air and the little straw thing that goes in the valve of the can -- blow it past the little hole in the venturi.