Accelerator pump tuning

[Jerry Clayton]

Gunner---I am generally called on to help out with tuning issues such as yours from 3 to 5 times a month-----The info I gave you will put you at a known referance base to start from---you are taking wild random shots at a basic tuning senerio---have it your way and good luck

Jerry

[Gunner]

Jerry, I appreciate your input, really! I think you're misreading my posts, though. I've done everything you suggested except swap out the power valve - which doesn't have much to do with low-speed, off-idle performance. I haven't touched the accelerator pump because I still don't have the parts to swap. I opened up the idle mix - suggested by two of you - for a partial improvement, and ran up the initial timing to no particular effect either way.

When I get the low-speed, off-idle, primaries issues sorted out I'll look at the secondaries, power valve and other top-end tuning. I'm waiting for parts on that end as well.

I'm also really limited on time - I have more time to sit here and yack about it than twiddle a screwdriver. It's frustrating.

[zrayr]

Originally Posted by Gunner

".............The interior of the distributor shows a lot of corrosion - the prior owner lived right on salt water . ..............."

my msd dist. also shows corrosion, even though I live in a dry climate. Works fine though.


Z. Ray

[Gunner]

Originally Posted by zrayr

my msd dist. also shows corrosion, even though I live in a dry climate. Works fine though.

I need to post a pic. It's not just "no longer billet-shiny" - it looks like something off a swamp boat. The magnetic pickup frame is rusted.

The weird thing is, it looks like corrosion from the inside. The interior base is heavily corroded, as is the lip... and then out from the lip about a quarter inch around and under. The rest of the outer base and the shaft down to the o-ring is fine. It's as if the cap was filled with acid at one time. Weird.

It's cleaning up nicely, though. I think it's perfectly good except for the visual aspect. I just didn't want any problems down the road; cheap insurance to replace it.

[Gunner]

EDIT: Never mind. Will repost after some more testing.

[patrickt]

Originally Posted by Gunner

No secondary action at all...

... and how did you make that diagnosis?

[*13*]

Did you figure out the problem? I was going to suggest looking for a bind in the linkage or something hanging up. Your picture shows a Holley mounted on the car. Did the prev owner change that out or is it a different car?

[patrickt]

Originally Posted by *13*

Did you figure out the problem? I was going to suggest looking for a bind in the linkage or something hanging up. Your picture shows a Holley mounted on the car. Did the prev owner change that out or is it a different car?

Hyde, I believe he has bolted on an entirely different carb. But, I also believe that his hesitation problem is still there, even with the new carb on the engine.

[*13*]

He said the previous owner claimed the hesitation. I assumed this meant the car came this way. Maybe I'm not thinking on the same plain If the rear butterflies are not opening on the carb (as he posted before he erased) this can only mean a few things. THe butterflies are bigger than the manifold hole, there is something binding or there is not enough air persuasion...presuming everything else is functioning properly.

[patrickt]

Originally Posted by *13*

He said the previous owner claimed the hesitation. I assumed this meant the car came this way. Maybe I'm not thinking on the same plain If the rear butterflies are not opening on the carb (as he posted before he erased) this can only mean a few things. THe butterflies are bigger than the manifold hole, there is something binding or there is not enough air persuasion...presuming everything else is functioning properly.

Yes, he wrote that the previous owner mentioined hesitation. But for two completely different carbs to have the same problem (and I'm pretty sure the first carb was a vac secondary too) then I'm going to go out on a limb and say the problem is probably not the carb.

[*13*]

Then what? The nut behind the wheel? Kidding... I hope he get's it resolved. Maybe he should hold an Engine tuning BBQ & we can all take turns driving & diagnosing it?

[Gunner]

I posted too soon, having insufficiently tested the secondaries. I know I was getting some action because the white spring (very weakest) gave that hoppity-hoppity bog when I put my foot into it. However, I put the original spring (a long yellow, NOT the plain that is specified in the literature) back in, put an index on the vacuum rod and went for another drive. No motion at all - not more than perhaps vibration movement of the index.

The problem here is that the plain spring is supposed to be stock; it's the third strongest. Instead, I find the long yellow in there - the third weakest. I've put the short yellow in, the one between the long yellow and the white, and will drive it tomorrow.

I also put on the 0.037 squirters and that again had a little effect on the bogging.

I need to get the carb into the secondaries before I screw with anything else. If the new vacuum spring works, I can start on the other tuning from baseline again.

Yes, this is a new carb. I have the Holley here if I need it but wanted a new carb, and a BG, before I started putting a ton of time and money into tuning.

[elmariachi]

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

[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.

[elmariachi]

How far out are the mixture screws at present?

[Gunner]

Originally Posted by elmariachi

How far out are the mixture screws at present?

I haven't touched them since backing them out a quarter. I think that puts them at around 1-1/8.

[elmariachi]

Originally Posted by Gunner

I haven't touched them since backing them out a quarter. I think that puts them at around 1-1/8.

In my opinion, that is nowhere near enough. If it were me I'd:

1. Remove the carb and reconfirm the position of the transition slots. On a Demon, if you have to even slightly tinker with those to get your car to idle, you will introduce a bog or off-idle stumble. Use the Idle-Eze to get the idle right (as much as 2 turns out) and as a last resort use the secondary idle screw if needed, but don't touch the primary.

2. Roll the mixture screws out to 1.75 and go drive it. With the leaner primary jets you should be able to start at 1.75 and then begin backing down closer to 1.5 as a final. Forget the itty-bitty mixture adjustments, roll them way out and see if it makes any difference.

Have you replaced the plugs in this car since you started? Do they look like mine below or do they have a black soot ring on the thread base?