The Stovebolt Site Forums The Shop Area Engine Shop Sticking on Idle

My 235 runs great but I notice that the carb tends to stick on slightly high idle. If you punch the accelerator, it will drop back down to normal. I've cleaned the linkage at all points with carb cleaner. Also, it doesn't look like it's hanging up anywhere. Is there any possibility this is caused by something other than a sticking linkage?

does your distributor return to its static setting after the vacuum advance mechanism advances the timing when you come off idle? the engine will idle a little faster if the distributor doesn't go all the way back and the timing stays a little advanced.

Check where the linkage goes thru the fire wall or the pedal hinge.


Pete

A worn throttle shaft and/or the holes in the carburetor base where the throttle shaft goes through it can cause the throttle plate to hang up on the housing. I've solved minor misalignment problems by loosening the throttle plate screws and tapping the plate into exact alignment with the bore with the idle screw backed off several turns. If the problem is caused by wear, it won't get noticeably better until the housing is repaired with bushings and the throttle shaft is replaced. This type of wear can also result in vacuum leaks around the shaft that can affect idle mixture and speed.
Jerry

Thanks for the replies. Tom, I hadn't thought of that and I don't know the answer. I guess I'll have to get under the hood and see what the vacuum advance does once pressure on the accelerator is released.
After my original post I thought of the place where the pedal linkage passes through the firewall, so I'll check that out.
Jerry, is it best to take the carb off to check for the wear you describe?

Yes, it's more evident when looking at the carb from the underside. Since the throttle shaft screws are peened over to prevent a loose one from falling out and ending up in the engine, only loosen the screws enough to allow the throttle plate to move around a little if you decide to do the plate-centering thing. Getting a loose screw into the intake can do some pretty significant damage.
Jerry

Check for the throttle lever to be loose on the shaft. This is pretty common on these. I weld it up with bronze welding rod. You need to remove the base from rest of the carb though. Remove the rod from the linkage at the carb lver & make sure it pulls down further. Sometimes it runs out of travel before the throttle is completely closed due to wear in the linkage.
There is an auxilary spring for this. It was a quick fix we used to sell many years ago. It is still available. Most parts stores have a card with universal throttle springs. These still come on it. It is a small spring with the loop on one end at a 90 degree angle. It hooks over the trottle speed adjustment screw & the air horn screw above it. It installs in seconds & can solve problems like this.

It looks like this was a case of the throttle linkage not returning all the way. I put a stiffer spring on and it solved the problem nicely. I did pull the carb and check the butterfly valve, the bushings, and the lever. The valve isn't sticking in the throat, no play in the lever, and there is a very small amount of wear in the bushings. I noticed that when the engine would stick on its usual slightly high idle, I could reach down, grab the accelerator pedal with my hand, and pull it up gently and that corrected the idle. So I just put in a stiffer spring. That seems to have done the trick. No binding at the firewall, by the way. Maybe the throttle return spring was just too weak.