Air Cut Off Valve problem

I have recently just rebuilt two carburetors for a Honda CB500T. I am having problems keeping it running below 2,000 rpms as well. I have noticed that the air cut off diaphragms are torn a bit and probably should be replaced, but I can find no new replacements ANYWHERE! What exactly do these do for the carbs and what are my options in fixing these? I am thinking about trying to patch them somehow with something light as an epoxy or something. Are there any replacement OEM diaphragms anywhere that will also work in this carb?


It will be hard to find brand new replacements for those diaphragms. However, if the tears or holes aren’t too big you can indeed patch them with a thin coat of epoxy. I have read of others using Plasti-Dip to repair them as well with good results.

The diaphragms are used to raise the slides and needle in the carb. The intake vacuum created when the intake valves open acts on the diaphragm and lifts ups the side allowing more gas to be released. The wider the throttle is open, the more vacuum there is, the higher the slide is, the more gas there is, the faster you go!


Evan Fell

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