Engine stuck at high idle

[nljakestoo]

I’ve got a 1939 Case RC. I just rebuilt the carb and set it to factory settings (triple checked). Engine hardly cranks over and fires right up. It drives ok but has a tiny bit of surging and the idle is high. The idle adjustment needle on the Zenith carb doesn’t affect idle at all. Not sure why. New gaskets around exhaust/intake manifold and rebuilt and changed carb gaskets. I’ve sprayed brake clean all around to see if it’s sucking air around these areas but seems solid. I even messed with the governor to see if perhaps it was binding but to no avail and no change in RPM. Kind of at a loss at what to do. The magneto is making a funny groaning noise and got super hot to touch when I ran it for about 20 min. Was rebuilt 2 years ago. Not sure if this is two seperate issues or what. Anyone have any ideas or rabbit holes to go down?

 

[greenmech]

I’ve got a 1939 Case RC. I just rebuilt the carb and set it to factory settings (triple checked). Engine hardly cranks over and fires right up. It drives ok but has a tiny bit of surging and the idle is high. The idle adjustment needle on the Zenith carb doesn’t affect idle at all. Not sure why. New gaskets around exhaust/intake manifold and rebuilt and changed carb gaskets. I’ve sprayed brake clean all around to see if it’s sucking air around these areas but seems solid. I even messed with the governor to see if perhaps it was binding but to no avail and no change in RPM. Kind of at a loss at what to do. The magneto is making a funny groaning noise and got super hot to touch when I ran it for about 20 min. Was rebuilt 2 years ago. Not sure if this is two seperate issues or what. Anyone have any ideas or rabbit holes to go down?

Do you have an adjustment on the throttle itself? Maybe set too high? Ron MN

 

[used red MN]

The idle adjustment needle on the Zenith carb doesn’t affect idle at all. Not sure why.

If you had it out did you center the throttle plate? You would have to pull the carb and look at the plate to see if it is sealing completely around when held shut. To center loosen throttle plate mount screws to the point where the plate can just move. Hold tension on the throttle shaft lever in the closed direction. Tap the throttle plate with the end of the screwdriver shank to center the plate and tight down the plate while continuing to hold pressure on the lever.

 

[Bob Bancroft]

If you had it out did you center the throttle plate? You would have to pull the carb and look at the plate to see if it is sealing completely around when held shut. To center loosen throttle plate mount screws to the point where the plate can just move. Hold tension on the throttle shaft lever in the closed direction. Tap the throttle plate with the end of the screwdriver shank to center the plate and tight down the plate while continuing to hold pressure on the lever.

And the throttle plate only goes in one way, and back the idle speed screw off when centering plate.

 

[Dick L]

And the throttle plate only goes in one way, and back the idle speed screw off when centering plate.

For idle the throttle plate only can be open a crack adjusted with the stop screw. Check stop screw setting with engine running holding the linkage back by hand to insure you do not have dragging linkage.
The throttle stop screw will needed to be adjusted together with the idle screw or (air mixture screw) to get to desired mix for idle.