cagotzmann

I give up with this 83770 Street Avenger on my ZZ383.
The main problem is a constant off idle stumble. Happens at any RPM below appox ~ 2500. Parked or actual driving doesn't make a different.

This has done this since day one. I can get it to work better some days than others. I think it may have something to do with the intake ( air gap 7516 ) since I have tried every combination of accellerator pump cams / discharge nozzles. (tried .28 - .37) tried every cam in setting 1 or 2. None eliminate the problem. Most make it worse not better. I also have a ARF gauge in both banks. WOT AFR's are 11.5 - 13.2,

I have also mis adjusted the accellerator pump lever to see the effect, this makes it worse ( delay hesitation big time ). I do not get any back fire, only stumble then zoom.

So what I see happening with the AFR at off idle I get a lean spike followed by a very rich spike, which tells me not enough gas then too much gas. If I had another carb I would switch it out to see if something else works better.

I also have a MSD 6530, so I can program any curve. I have tried more advance at the lower RPM, and less advance. Doesn't make a difference.

While driving it happens in any gear (manual) 1-6. more noticable in the lower gears.

Vacuum at idle at 800RPM ~ 18

The power value I have tried stock 6.5 and a 8.5. No difference.

This is a vacuum secondary carb so the secondaries dont kick in unless the engine is loaded. So during a parked quick throttle opening it also stumbles.

Anyone in the Edmonton (canada) area with a spare carb for me to try ????

Flyinace3

I had those same issues with a 650 double pumper. After tuning and even being sent to a pro the issues were no better. Installed a quick fuel 650 dp and all those issues are gone. I messed around for a year and a half trying to get it cured to no avail .

Haggisbash

Are the butterflys adjusted correctly? Read Lars paper on setting these, I had a stumble or flat spot just off idle and setting the butterflys correctly cured this. It is common for the problem to be misdiagnosed as an accelerator pump issue.

Bad Bird

Is the transition slot correctly exposed?

Bhus

I had the same problem with my Holley 670, and setting the butterflyes cured it.

gungatim

As noted, download Lar's paper on carb tuning Holley's, he explains in detail how to adjust and in what order to eliminate the problem...If The guy would publish a book,they could just go ahead and turn off the internet...

cagotzmann

THe only lars papers I found are for a q-jet. But the transition slots are equal on both the primary & secondary side. When Closed only only portion that is exposed is above the butterflies ?

chevymans 77

If I'm reading your post correctly and there is no transition slot exposed at idle on the primary side then that is more than likely one of your problems.

Does it have the stumble at 3000 rpm and above?

2500 and below you are still on the idle and transition circuits.

It sounds like you've played with the pump cam and arm setup while this would be the first place to look and most common to cause the issue you are describing you've covered it.

Neal

cagotzmann

No the transition slots are clearly visable from on top at idle. When the butterfies are closed they are just at the bottom edge of the slots. No exposed slot from the underside.

at 2500 and below it can be any gear 1st through 6th. In 1st it would not be in idle the gas needs to be pressed to get to 2500 RPM and I would be driving about 24 MPH.

Doesn't happen if I ease into the throttle. ?

Haggisbash

I haven't got access to the papers at the moment but if my often faulty memory serves me well isn't there supposed to be 20 thou of the transition slot exposed beneath the butterflies with them closed and both the primary and secondaries should be exactly the same. Any adjustment to one has to be matched on the other.

Haggisbash

I found Lars paper called - Technical Information Bulletin Rev. F 4-2-13
How to Tune a Holley
(basic)
I was correct there should be 20 thou of the slot exposed beneath the butterfly when it is closed.

flyeri

I missed all of last summer driving the 68 because of similar issues with a Ultra DP 750 that ran fine for several months then started running bad. Thought bad gas, so I went through that whole process. Then ignition, and swapped systems back and forth. The stumble would always come back. Inspected for broken valve springs, vacuum leaks at intake and base plate, new HEI, new engine. Still had the stumble, only worse. rebuilt carb again. Still stumbles. Put on Edelbrock 750 (1411) and stumble is gone. Will not go back to Holley.

resdoggie

Yes. Expose 20 thou on the primary side so the exposed portion of the slot from the underside should now look like a square slot. This should be pretty close to 20 thou. Then turn the carb upside down and adjust the secondary side, by eye using daylight, to the same butterfly opening amount as on the primary side. Iirc, the secondary transition slots are not in the same position as the primary side and by adjusting the secondary side to 20 thou will open the butterflys too much. Once done, any further idle screw adjustment must be the same for both the primary and secondary as Hagg pointed out.

To the OP, if you still have problems, you can donate the carb to me.

condor7

Thought I would chime in. I am using a Holley Avenger vacuum secondaries, on my built 355 with hydraulic roller cam set up, Air Gap, Supercomp headers, MSD ignition and so on. My carbrurator was working fine out of the box some 10 years ago. Then had a horrible lean condition when going to get gas one day. Got it back home and did a little trouble shooting. Come to find out that the primary throttle shaft wore out and was leaning one bank to the point of misfires. Happened all of a sudden, no warning. Put a new base plat on it and thought everything would be fine. Nope, still had issues. Tossed it aside for a Quick Fuel, Street Slayer, I think. Anyway the QF leaked fuel and just was a bad overall experience to the point I sent it back after discovering the main body was a PROFORM. May be just my dumb luck but the QF was nothing but a headache. Went back to the Holley determined to get it right. Found all of the Lars papers and set up the carb. Had the same issues with the stumble. No issue with the accerator arm or cam. Pulled the carb back off and went to the throttle blades. Sure enough the secondaries were not matched to the primaries. Set the transition slot on the primaries, the secondaries are Different however.

The transition slot is higher in the venturie area so using a feeler gauge is not going to work. Placed the carb over a bright light to see the difference, adjusted the secondaries to show the same light as the primaries. (As described in Lars papers). Put the carb back on and had a very noticable difference to the good. Now when making any adjustment to the primaries for say bumping up the idle a little, the same amount of adjustment is required for the secondaries. I appearantly read over this part. It is clear in Lars papers. I only make 1/4 turn adjustments to both and then observe my A/F gauge. The engine is very happy now and is running great. 68 jets in the front, 76 in the rear. 6.5 power valve with 14 inches of vacuum at idle. Replaced the float bowls with upgraded ones with the glass sight and they are more resistant to the ethonal in our fuel. Idle screws absolutely make a difference in idle so I know I am in the idle circuit which is also the cruise circuit. I go down the road at 15.1 A/F at 75 MPH.

Just thought I would share my experience. Seems lots of people have issues with various carbs. Mine was with the Avenger and a QF unit. Not bashing either, just took the time to look closely and re-read Lars papers. My issue was more of a self inflected wound rather than a carb that would not work correctly. Hope that helps a little.

Regards.

chevymans 77

flip if over and looking from the underside you should see around .020" of the slot below the Primary throttle blade.

Once set put it back on the car and take it for a test drive without adjusting the idle speed screw more than a 1/4 turn.

These carbs are known for being setup lean and will cause the issues you are having.

If the off idle stumble is gone but the cruise stumble is still present then set the idle mixture screws rich and try again. If this takes care of the cruise stumble then the transition circuit is lean.

give this a shot and report back what you find.

Neal

cagotzmann

SO I spoke with "Holley tech support" Here is what they said

1. there should not be any part of the transfer slots below the plate.
2. My carb is to large for the ZZ383
3. The jets are to lean in both the primary / secondaries
4. Dont trust AFR readings they dont work on Carb engines ( read the plugs) Ok with the stock out of the box they were jet black. Next was a transfer to the warranty department.

The next problem I was on hold for too long and hung up. I hope it doesn't come to a replacement, because it I may end up with EFI.

I will see about adjusting the butterflies to see if there is any changes.

commander_47

I have a 670 street avenger on my 383 build.

I moved the front jets to the rear, installed three sizes bigger on the front, and replaced the stock 31 squirter with a long reach 34.

Had to slow down the high idle, and set the mixture with a vacuum gauge.

Car is a rocket. No hesitation at all.

Carb was a little lean, not now.

The street avenger is a pretty user friendly carb.

Make sure you set the mixture with a vacuum gauge. Black plugs is not good.

Make sure your squirter is up to the task. If your squirter is too big it will bog down and turn the plugs black.

JimT

I threw mine in the garbage. Nothing but trouble since new.
Good luck!!!

commander_47

Don't toss em, send them to me. I'll pay shipping.

Bad Bird

What a load of crap. Engines are not magic, of course you can use an AFR gauge with a carbed engine.