Jim85IROC

iTrader: (2)

I'm helping a buddy with his car, and wanted to post for advice here. It's an 83 camaro, with a new zz4 and a th350. 1 3/4" long tube headers, !cats, true dual 2.5" exhaust.

Right now he's running a 4160 600cfm holley, and the plugs are showing that it's running lean. He's also got a nasty bog when he floors it. He's tried playing with the accelerator pump cam and it's helped a bit, but hasn't solved the problem. Right now he's using a green pump cam at position #1 and a .035 squirter.

We think that a 2-step approach is in order. First, we think we need to increase the jet size, and secondly, we need to provide a good deal more fuel enrichment at WOT.

Right now we feel that we're a mile out of the ball-park, and are hoping for some suggestions that can help us get it close so that our tuning time can be better spent getting it perfect. Anybody have a suggestion for what size jets we should try, and what else we should do to eliminate the lean condition, and eliminate the lean fuel enrichment condition?

Unfortunately, I'm an EFI guy, so I know virtually nothing about carbs. My friend is far more carb educated than I am, but it's still a big learning process for us both. Any help would be appreciated.

Oh... he's also got a 750 80508 (basically a 3310 with an electric choke) that he's had sitting around for a while. He also plans to rebuild that and try that carb before he goes too deep into his 600 carb. Any baseline recommendations for that one?

duckmanquacker

If you can give some more specs on the carb (IE main jet size, powervalve size, rear jet or plate size, etc.)

Jim85IROC

iTrader: (2)

I'm not sure he's got that info. It's a 4160 that he bought new from Summit and hasn't changed anything on, except for the pump cam and squirter.

edit: From what I can find in the holley instruction manual, the carb came with a 65 primary jet, a .031 pump discharge nozzle, and a 65 primary power valve. The secondary plate is a 34R9716-6. Not sure what size that translates into.

five7kid

iTrader: (14)

What's happening is the secondaries are opening too quickly. Holley offers different diaphragm springs to help avoid that, in this case meaning you need a stiffer spring. But, that also has the effect of reducing the max opening of secondaries (potentially, depending upon your engine size and max RPMs - a 600 on a ZZ4 will probably open fully eventually).

Instead, get a Quick Fuel Technologies adjustable vacuum secondary housing. http://www.summitracing.com/parts/QFT-63-1/ What the QFT unit does is meter the vacuum signal to the diaphragm to control the opening rate, which is what you really want to control, without affecting the max opening.

Jim85IROC

iTrader: (2)

Thanks. I'll pass that on to him.

Jim85IROC

iTrader: (2)

My buddy found that his main jets are 122-622, but we can't find any information that translates that part number into an actual jet size. Anybody have a cross-reference table for the part numbers or know what size those jets are? I can't even find that part number on Summit.

It seems that everything on this 4160 carb is as non-standard as it gets.

five7kid

iTrader: (14)

Those are #62's. "122" is their prefix for their standard main jets. The last "2" is supposed to indicate a high precision orifice, I believe. Type "hly-122-62" into Summit's search field and you'll get a hit.

http://www.holley.com/types/Jets%20a...r%20Bleeds.asp

Jim85IROC

iTrader: (2)

Thanks.