Idle speed will not stay set on zenith

DeBordEngineMan

DeBordEngineMan

Senior Member
Hey guys have been working on the overheating problem on the Tudor as a lot have seen. My problem now is I can let the car warm up good and set the idle speed on my newly rebuilt Zenith and I will stop in a little while and the car's idle speed has gained and I have to get out and reset back down just to have it rev right back up in just a few minutes the screw must be turning on it's own but not for sure? Reset and it go's right back were it should be idling right, anybody have a fix for this, maybe get adjusted were you want after the car warms good and put Locktight on screw or maybe I am just doing something wrong? Thanks for any help, Robert DeBord
 
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If it is a set screw problem then I'd try some trim adhesive as opposed to the locktight. The adhesive will stay slightly plyable where as the locktight will act more like a glue. I've also heard of using honey believe it or not but I have never tried it. You can also bugger up the set screw threads just slightly for good results. I'm not sure I'm convinced that it is the set screw being the problem.

Is the throttle spring pulling the linkage back tight against the stop screw? Just pull against the linkage when it is idling fast and see if it is back snug.

Is it possible you have a vacuum leak?
 
The reproduction shafts have a couple of problems that need to be addressed before installing them, which may be causing the problem you are experiencing.

The idle adjust screw is supposed to be tight and difficult to turn. If it is not put the corner of the bracket the screw is mounted in into a vice and squeeze it more until it is tight.

The curvature of the arm is not bent out far enough and it can cause the throttle rod to rub against the choke rod. Clamp a corner of the arm bracket in a vice and with vice grips bend the arm further out. Be careful not to put pressure on the brass shaft where it is swaged to the arm bracket as it can be torn loose.

Right where the brass shaft is swaged to the bracket, the first 1/4" of the brass is usually found expanded by the swaging process. If new bushings were installed in the housing and reamed to fit the shaft it is common to find that this last 1/4" will want to bind in the housing bushing. Clamp the shaft in a drill press and with some emery paper sand the shaft in this area until there is a smooth fit with no binding.

It is important that there be absolutely no slight binding when the shaft is installed and the carburetor is cold. At engine temperatures it will expand and bind more and it will have difficulty returning to the proper idle.

Tom Endy
 
Robert, check the bind of the screw and if it is not pretty tight you can grab the arm where the screw threads into the arm and pinch it with a vise grip to give it more bind. The screw hole is just metal rolled over and threaded so it will compress easily and make the screw tight.
 
Make sure the throttle bracket on the flywheel housing is not rubbing against the fire wall. Make sure all bolts and arms are tight,including steering coloum.
Have you taken the car for a spin around the block yet? If so,did it back fire or pop when you backed off the gas? (air leak)
Be sure to check your timing and points also,sometimes its not the carb.
 
Thanks James I see what you were talking about the metal folded over and threaded just gave it a good squeeze with the Vise grips and the set screw stayed were I set it thanks for the real easy fix, Robert DeBord
 
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