Quick Carb Tuning Question
Thread Starter
Pro
Joined: Apr 2007
Posts: 736
Likes: 1
From: Chester VA
Quick Carb Tuning Question
Just installed a 670 Holley avenger. Along with an ignition upgrade it really woke the car up. Having one small problem, wants to stumble when I crack the throttle, idles fine, once you get moving or open the throttle more it runs great. This is under normal take offs, haven't been able to try a real launch since it'll bog bad if you crack the throttle fast. I looked for a vaccum leak but found none, idle mixture seems OK, Pump cam maybe?
Drifting
Joined: Apr 2003
Posts: 1,698
Likes: 9
From: Johnson City TN
I had the same issue. A larger accelerator pump nozzle helped mine - I believe I ended up at 3 sizes larger. I've also read that a different pump cam may produce a similar result, but I haven't tried that approach.
Instructor
Joined: Feb 2006
Posts: 240
Likes: 0
From: Allentown PA
How to tune a Holley...go to the top of the page...click on "other" then click on "Tech Tips" then click on C3, then "How to Tune a Holley" by Lars...its step by step how to get it right...
I had the same stumble...just followed the precedures and made adjustments accordingly...I now have instant response at anytime I decide to mash on it, at any RPM.
The only thing I noticed was missing from the article was specific to the Street Avenger series carbs...on a later post I saw from Lars he said that the Street Avengers ran lean out of the box...which I will attest to...I had to move up 4 jet sizes from the ones that came with it...I also saw a post from Lars that said the secondaries should be about 8 sizes larger than the primaries...also good info...in my particular application I had to move up 3 sizes larger in the shooters(nozzles)..the stock cam was fine and then changed to a lighter secondary spring...it took some time to get it right, but well worth it.
Also, there was articles on distributor vauum controls and timing for performance..they all work together ofcourse...check'm out. Worked for me...
I had the same stumble...just followed the precedures and made adjustments accordingly...I now have instant response at anytime I decide to mash on it, at any RPM.
The only thing I noticed was missing from the article was specific to the Street Avenger series carbs...on a later post I saw from Lars he said that the Street Avengers ran lean out of the box...which I will attest to...I had to move up 4 jet sizes from the ones that came with it...I also saw a post from Lars that said the secondaries should be about 8 sizes larger than the primaries...also good info...in my particular application I had to move up 3 sizes larger in the shooters(nozzles)..the stock cam was fine and then changed to a lighter secondary spring...it took some time to get it right, but well worth it.
Also, there was articles on distributor vauum controls and timing for performance..they all work together ofcourse...check'm out. Worked for me...
Last edited by OldCorvetteKid; May 21, 2007 at 01:56 PM. Reason: for other useful articles
Pro
Joined: May 2006
Posts: 576
Likes: 0
From: Kernersville North Carolina
if i'm reading correct...? it seams i'm having the same issue. when i flick the throttle from idle to full fast it will stumble...what is the accelerator pump? i have a 650 holley double pumper.
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
The Holley Street Avenger carbs are jetted too lean out of the box. Increase primary jet size 2 to 4 jet sizes, and then jet the secondary size 8 sizes larger that the resulting primary. This will cure the stumble and produce much better power and throttle response.
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