Thread: ZZ4 350 stutters on acceleration...cold weather?

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Well I rushed home from work to take the car for a spin while it was still warm outside. The stutter was still there but less than the other day. So I decided to richen the mixture a bit by turning out the idle mixture screws. It helped quite a bit, but still not 100% (i tried turning them in first and the car immediately idled like crap). I guess its true that the car needs more fuel in cold weather? And I guess what HWORREL said about having exhaust warming the intake would make a big difference since it makes the car "immune" to the cold air outside.

Are the idle mixture screws only for low rpm as the name implies, or does it have some effect on higher rpm as well?

Thanks for all your input guys

Not exactly right, it needs to vaporize the fuel thats there instead of entering the combustion chambers as a liquid instead of a gas. Those screws affect the idle mixture only..

If your idle screws and throttle plates aren't adjust properly it can cause what is called tip-in hesitation. You can get the idle rpm's right with the throttle adjustment screw but idle mixture (that some say doesn't effect any other circuit) won't be right. If the throttle plates are open to much, at idle, you can get the bog you are talking about.

Originally Posted by Mikej

If your idle screws and throttle plates aren't adjust properly it can cause what is called tip-in hesitation. You can get the idle rpm's right with the throttle adjustment screw but idle mixture (that some say doesn't effect any other circuit) won't be right. If the throttle plates are open to much, at idle, you can get the bog you are talking about.

Originally Posted by DennyW

Mikej, I wish you would get this correct. The idle circuit, IS just the idle circuit.

Maybe it would be good to go read this page, and pay close attention to the idle, and transfer circuits.
http://www.chevyhiperformance.com/te...uretor_basics/

The most likely problem he is having is lean mixture, accelerator pump not working when he opens the throttle plates, or the fuel level needs to be raised another 1/8". (raise the fuel level, if Holley, until the fuel just wants to trickle out the threaded hole). Also, depending on the model, the front bowl fuel level hole is at a different height than the secondary bowl. If you mix the bowls up, your fuel level will be off. And make sure the carb is level before you adjust anything to do with fuel levels.

And like HWORRELL says. It can also be a heat problem. The engine is intended to run at normal operating temp. Until it reaches that, it can run a little lean, causeing the fuel not to vaporize properly. If the fuel does not vaporize, it will remain in droplets, and cause you to be lean.

If the idle circuit doesn't have anything to do after just idleing what is this pertain to?

"The idle circuit is fairly simple, yet has a dramatic effect on street manners, idle quality, emissions, and fuel mileage."

This quote was taken off the site you suggested. And I do know about the transition slots. If you have the throttle plates open to far at idle you bypass the circuit. If you know how the carb works, you know why your making the adjustment.

Denny, I'm sorry that I'm not very good at explaining things on a key board. My main point was Lean Drop Method of adjusting idle and position of the throttle plate vs yours using the vaccum guage. Both will work. Next time I'm playing, my old car, I'll try your way.