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I'm having a problem with a sticky idle on my Holley 3367. I recently put a kit in it and it runs well. Idle just seems to stick when I apply light throttle, maybe 1200 or 1500 rpm. It just won't go down. Here is what I think I know...
Fast idle cam is not holding the idle up. Completely free.
Moving the choke makes no difference.
Sprayed cleaner in the primary bores and wiped edges of the throttle plates.
I can blip the throttle and it will go down to regular idle speed.
Increasing the spring tension helps but I'm afraid that I'm at the point where if I add more tension it will become jerky when I start.
When the engine is not running the throttle snaps back like it should. This only happens when the engine is running. If it is sticking at say 1200 rpm and I turn the engine off the throttle snaps shut. Can the blades be held open by airflow? I'm out of things to try so any help would be appreciated.
Looks like the spring is a bit weak. I also hooked the spring in the end of the accelerator rod instead of the holes below it. This is shown in Figure 8C or the Chevrolet Chassis Service Manual page 6M-7. That increases the spring tension and also the leverage on the throttle shaft.
I added the second spring like the later Chebbies for safety as I had an experience with a 396 where the throttle spring broke and the engine went wide open, but that was many years ago. For what it is worth.
Remove the spring from the engine connection and hold it another 2" stretched away from the carb. See if that will consistently return the idle to where it should be - if so a stronger spring would be in order.
Something I discovered after 40 years with my '67 is that the accelerator rod was put in backwards. I don't know what orientation yours should look like, but wouldn't hurt to double-check.
One more thing. My '72's accelerator felt very twitchy; when I put on a stronger spring, it actually made it smoother and more controllable.
Jeff,
I would start by ordering the correct throttle return spring and install it through the hole in the accelerator rod. Also, the white nylon washer that the accelerator rod goes through should be installed from the reverse side of where it currently is installed. The nylon washer keeps the return spring from wearing on the rubber bushing. See pic below.
I will order another spring and change my bushing. Sounds like everyone thinks it is just a weak spring issue, and I hope it is. But why would the throttle snap closed as soon as I turned the engine off?
Also check the spring on the primary throttle shaft is properly installed. From your description and pictures, I believe it is, but worth a quick look. Chicago Corvette picture of throttle plate assembly for Holley #3367, 3370 carburetors
I will order another spring and change my bushing. Sounds like everyone thinks it is just a weak spring issue, and I hope it is. But why would the throttle snap closed as soon as I turned the engine off?
What holds the throttle open is friction between the throttle shaft and the bushings in the carburetor base. This friction is caused by engine vacuum pulling the throttle plates which, in turn, forces the shaft hard against the bushings.
The shaft and bushings should be round. However, as the throttle shaft and the bushings wear they become less round and shaft rotation becomes more difficult.
You might bandaid this with a stronger return spring. It's worth a try.
A better solution would be to replace the throttle shaft and re-bush the carburetor base.
I see this same phenomenon all the time on Rochester Fuel Injection which has a huge throttle plate. Engine vacuum generates many pounds of force on that plate which results in significant shaft and bushing wear.
What holds the throttle open is friction between the throttle shaft and the bushings in the carburetor base. This friction is caused by engine vacuum pulling the throttle plates which, in turn, forces the shaft hard against the bushings.
The shaft and bushings should be round. However, as the throttle shaft and the bushings wear they become less round and shaft rotation becomes more difficult.
You might bandaid this with a stronger return spring. It's worth a try.
A better solution would be to replace the throttle shaft and re-bush the carburetor base.
I see this same phenomenon all the time on Rochester Fuel Injection which has a huge throttle plate. Engine vacuum generates many pounds of force on that plate which results in significant shaft and bushing wear.
Jim is correct as usual.
I found the primary throttle shaft would move quite a bit in the direction parallel to the spring. I purchased the kit with the pilot drill and brass bushings as well as the screws and nylon bushings. I was surprised that the primary shaft had smaller width bushings than the width of the reliefs in the shaft and the secondary shaft had no nylon bushings at all even though it had reliefs in the shaft. I guess I went overboard as I purchased a roll of nylon and made new bushings of the same width as the reliefs for both shafts. Replacing the bushings as well as flattening the warped throttle baseplate resulted in the best performance of a Holley on a street vehicle application I have ever obtained, not that I am bragging, but I guess I am
First, check the movement of the primary throttle shaft to see if you have this problem. If the movement of the shaft perpendicular to the spring is greater than the movement parallel to the spring, you have wear.
So I increased spring tension and the carburetor now seems to return to idle. I'll drive it a little more to see. I did check the floor mat, no problems there.
I also checked shaft play in both parallel and perpendicular directions to spring travel. Based on what I was hearing here and reading I was expecting to find movement but did not find very much in either direction. That probably doesn't rule out a possible bent shaft or some misalignments with the butterflys and throttle bores however.
So this winter I am planning on removing the carburetor and checking bushings, alignment, and the shaft more thoroughly.
I just got this car running after a 10 or 12 year hiatus for paint, engine work, etc. and we're running out of summer soon.
Thank you all again for your help.
Last edited by milano maroon; Sep 21, 2025 at 03:23 PM.
Reason: grammer
I had a Holley that had a lot of shaft wear and resolved the problem with a second spring from the bottom of the throttle lever to the coil bracket at the rear of the engine. The rear spring changed the force vector on the shaft to help center it. It took some playing with spring tension of each to obtain the desired pedal pressure. Not the right way to fix it, but it worked. I added the back spring for demonstration only.
P.S. Milano Maroon is the best color. I might be a bit prejudice.
Sticky Throttle
