On the new Holley carb I have noticed something very different. On the choke housing toward the front of the carb is a hole that is covered in sometype of putty. My putty has come out and inside that hole is a screw. According to the Holley manuel I have that screw does not have a name. Anyone have a idea what this screw does?

Wondering if this screw is a screw to adjust the fuel mixture or the choke itself.

The small screw in the integral choke housing for the 4160 Street Avengter carb is the adjustment screw to set the proper location of the choke piston inside the choke housing.

Rod

Thanks, what would be the proper location of the choke piston? How would I adjust this? Never tuned one.

Aaron,

The adjustment is set at the factory and something you don't normally have to mess with. Go to the Holley website and look up technical documents for the tuning of a 4160 carb and you will see how the adjustment of the choke piston is supposed to be made using a paper clip to measure the gap space. I don't have the actual web page address handy but you can find it under the technical support section of the Holley website.

Rod

I have a 770, I belive that the Avenger carb is a 4150 type carb, as it has the metering block for the front and back bowls with removalbe jets. The 4160 carbs have a rear metering plate.

You're right, my mistake. I don't know why I said 4160, but I think the Holley tech support tune-up notes on the website are basically the same for both the 4150 and 4160 carbs.

Rod

Would the screwing in and out of the screw change the factory setting of the piston? The holley tech info is not clear to me. If this is the case would this affect idle quality?

Let me start over and explain my problem. I have a zz4 crate motor with only around 15 to 20 miles on it. I have the 670 Street Advenger on it. I currently have open headers. I know this is not good, but I drove it from his shop over to mine (rural area). I started messing around with the mixture screws and this choke piston screw trying to cure a high idle that is related to the trottle blades. I'm a novice so I really have no idea what I'm doing. My mechanic installed the motor and carb. Well, once I did this I got a very mushy pedal and the carb backfires now and breaks up all over the place. I know I screwed something up. Did I burn a valve, hopefully not. Did I blow the power valve? Do I need to recheck the float level?

Aaron,

I first got my 670 Street Avenger carb a few years ago when they first came out. My engine is a 400 hp 327, so the carb was not a simple "plug and play" for me as Holley advertises. I had to do several modifications on my carb to get it to run just about perfect now, including fine tuning it with an air/fuel ratio gauge, richening the transition circuit, etc, etc. I initially had problems with the electric choke not fully releasing the fast idle, causing the engine to idle at about 1200-1400 rpm, especially after a long drive on the freeway. Holley recommended a fix for me but I later heard that the problem was corrected on the later carbs. My recommendation at this point in time would be to wire the choke open and take it out of the equation until you get the idle circuit and throttle setting first. Another thing, make sure that the idle mixture screws are the same number of turns out on each side. Start again by putting everything back to the initial factory settings and go from there until you get the engine to idle correctly without a stumble during off-idle acceleration.

Rod

Hotrod65SS

After consulting the Holley manuel on the web. The adjusting is not done with a paper clip. The older style 4150 are, but the newer 4150 style use that screw in the housing. Not sure what the factory setting of it is.

I had a question about the size of the idle feed restrictions when I first got my Street Avenger. I e-mailed tech support at Holley (on the Holley website) and they responded the next day. Send them your detailed questions about the choke housing adjustment and tech support should be able to help you out.

Rod

Aaron,

Oh by the way, the adjustment is not done with the paper clip, but I believe is used to measure the size of the gap that is required within the choke housing . The screw is used to adjust the distance of the choke piston to get the proper gap.

Rod