Stumble off idle -

[Grubby]

UPDATE:

Outside temp was near 70 today.

My car has 70 IAB. I ordered 66, 62 and 58s to try. The 84 main jets are still in place. Started with 80s.

Changed to 66 IABs and the car would barely run down the driveway and the the surging at steady cruise was much worse. The surge extended up to about 2400 rpm.

This was a successful test. I was able to make the condition worse. So, I must have gone the wrong way on the IABs.

I plan to order 76 and 80 IABs and see how that goes. As much worse as the car felt with 66s, I will guess going to something like 74s might be enough, but I want to move enough each time see the change.

John

[blykins]

IAB's control air, IFR's control fuel.

If you were stumbling right off idle, which indicates a lean condition, you went the right direction with the air bleeds. Something else is amiss...

[Grubby]

Brent,

My primary problem before this change was lean at steady cruise between about 1600 and 2200. That condition is now much worse and the rpm range where it happens got wider. This is the top of the idle circuit range.

IABs control lean/rich at the top of the idle circuit and also how high the top of the idle circuit goes.

The problem of trying to drive down the driveway at less the 1500rpm arose with the IAB change.

Correct me if I am wrong. I think the IFR controls the low range of the idle circuit. If correct idle can't be achieved wth the idle mixture screws then IFR needs changed.

If I put the IABs back to original 70s I would not have a problem in the lower ranges of the idle circuit.

The ranges my problems are in are not even close to the ranges controlled by the HSABs, so I see no need in messing with them.

About the only thing left to do is go the other way on the IABs.

John

[blykins]

You are correct. You were lean at the top of the idle circuit. IAB's control lean/rich at that area. You richened that circuit up (smaller hole, less air) and it got worse.

We have introduced an additional problem, but still didn't fix the initial problem, right?

[Gaz64]

May have been rich at the top of the idle circuit.

Go up to 74 IABs as first test, if it gets better then maybe drop your IFRs and try the original IABs.

How far out are your mixture screws now?

[patrickt]

Originally Posted by blykins

You are correct. You were lean at the top of the idle circuit. IAB's control lean/rich at that area. You richened that circuit up (smaller hole, less air) and it got worse.

We have introduced an additional problem, but still didn't fix the initial problem, right?

Brent, let's just suppose that Grubby's problem is not fixable by changing/adjusting the carb. And, remembering that the highest vacuum reading he could muster was 7", what scenario would result in the conditions he's seeing and be consistent with the low vac readings?

[blykins]

Well, it could be a few things....

I can't remember his cam specs exactly right now, but it didn't stick out as a big cam to me. However, the overlap and ICL it's installed on can play a role of course.

I think the Quick Fuel carb will make a noticeable difference though once he gets the stumble ironed out. I think he's on the right track...

Another thing to watch out for John, is that if you have raised the idle speed at any point in time, you possibly could have put it into the transition circuit if you adjusted it all on the primary side.

[patrickt]

Originally Posted by blykins

Well, it could be a few things....

I'll betcha a bottle of cam break-in goo that if he removes the breathers from both valve covers, fires it up, and puts his hands over the holes he'll feel the leak. Or use aluminum HVAC tape over them to see the suction. That's what we used to do when we were young, dumb, and broke.... If it tries to suck the tape in to the valve covers then he can tweak the carb 'til the cows come home and he's not going to fix the problem.