Holley 4412 Carb tuning

[GBCustoms]

Hey guys, I got my 66 burb running and it will idle fine and do ok if you slowly increase throttle. If you try to quickly full throttle it, it almost dies then backfires out the carb. I am completely ignorant when it comes to carbs, any suggestions. Thanks in advance!!

[bigblockv6]

I experienced the same symptom on my 68 305E with Holley many years ago, turned out I had the timing set wrong

[GBCustoms]

Thanks Ill do some testing.

[James]

Sound to me the accelerator pump discharge nozzle is too small or not working. Holley sell different size nozzles if the one you have is squirting. The specs sheet states you have a .028 I would try about a .032 to see if it improve. Here is a list of what Summit Racing has to offer:
https://www.summitracing.com/search/...rder=Ascending

Here is a list of specs for the 4412 (among other carbs.) showing what size nozzle and other spec that came with you carb:
http://documents.holley.com/techlibr...al_listing.pdf

Here is some tuning tips from Holley:
http://documents.holley.com/199r7950-7rev7.pdf

Here is some accelerator pump tuning instructions:
http://www.racingjunk.com/news/2015/...elerator-pump/

I hope this will help and not be information overload.

[GBCustoms]

Originally Posted by James

Sound to me the accelerator pump discharge nozzle is too small or not working. Holley sell different size nozzles if the one you have is squirting. The specs sheet states you have a .028 I would try about a .032 to see if it improve. Here is a list of what Summit Racing has to offer:
https://www.summitracing.com/search/...rder=Ascending

Here is a list of specs for the 4412 (among other carbs.) showing what size nozzle and other spec that came with you carb:
http://documents.holley.com/techlibr...al_listing.pdf

Here is some tuning tips from Holley:
http://documents.holley.com/199r7950-7rev7.pdf

Here is some accelerator pump tuning instructions:
http://www.racingjunk.com/news/2015/...elerator-pump/

I hope this will help and not be information overload.

No that is great, cuz I got it timed to the mark on the balancer, and it is still doing it. So timing is not the problem. I have a rebuild kit for the carb so I think that is next on the list then go thru the full carb tuning process. Thanks for the info!

[TJ's GMC]

Sounds like a symptom of already mentioned timing, probably not enough advance. Or the carb is set to lean, Careful with letting that thing backfire or you'll blow the power valve if you haven't already.

[GBCustoms]

Originally Posted by TJ's GMC

Sounds like a symptom of already mentioned timing, probably not enough advance. Or the carb is set to lean, Careful with letting that thing backfire or you'll blow the power valve if you haven't already.

Yeah thats what i was told so I bought an extra plus the one that is in the rebuild kit. I have the timing right on the balancer mark, but the problem remained when i advanced or retarded a few degrees. So I will do the carb rebuild and then go thru the full holley tuning. Side note, i picked up a 77 C10 for $450 to steal the front suspension and disc brakes off of. also have the ECE drop spindles w/ 6 lug rotors, rear drum rebuild kit, and the 4" drop leaf springs!

[James]

Originally Posted by GBCustoms

Yeah thats what i was told so I bought an extra plus the one that is in the rebuild kit. I have the timing right on the balancer mark, but the problem remained when i advanced or retarded a few degrees. So I will do the carb rebuild and then go thru the full holley tuning. Side note, i picked up a 77 C10 for $450 to steal the front suspension and disc brakes off of. also have the ECE drop spindles w/ 6 lug rotors, rear drum rebuild kit, and the 4" drop leaf springs!

Nice find.