Sticky high idle, carbs? ignition?

[mgmaniac45]

My 72 CB350 had no carbs, so I ordered 2 different sets off eBay and both sets had broken butterfly’s . No finding just the butterfly’s, so I got a pair of Nibbi 28’s with new manifolds and foam filters. Installed them, played with the jets and settings and it runs. Problem is it takes a while to warm up and it idles at 1200, but when I rev to 3000, it jumps to 4000 and won’t come down. Gotta turn it off to stop it. Any suggestions? If anyone knows where I can get replacement butterflies, I’ll switch to originals. Thanks

 

[EzPete]

Have you checked your advance unit? Sounds like it's sticking at full advance.

 

[stl360+450]

Problem is it takes a while to warm up and it idles at 1200, but when I rev to 3000, it jumps to 4000 and won’t come down. Gotta turn it off to stop it.

Sometimes if you flip the kill switch to off and then back to run you can settle a high idle.

Do you know how to check for air leaks? One way that I like is to mist water on the carb boots. If the water gets sucked into a spot where there is a leak, the engine speed should go down momentarily. If you can notice any effect, it likely means there is a leak.

How do the boots fit the carburetor throat? The indentation on the carb throat should match up with the bump inside the boot. It might be informative to share a picture comparing the throat of the OEM carb with one of the Nibbi carbs.

If anyone knows where I can get replacement butterflies, I’ll switch to originals.

Can you show exactly which parts are broken? It sounds like you are saying the throttle plates are broken, i.e., the flat circles that are screwed down on the throttle shaft in the carburetor bore.

Which series carbs do you have? 722A? 3D?

 

[mike in idaho]

Have you checked the spark advancer, for sticking?