There is no performance improvement for the 500 carbs with the air cutoff valves. The purpose of the valve is to enriches the idle circuit when the engine decelerates. What it does is cut off the pilot air to the idle circuit. This is like closing the pilot air screw every time you close the throttle when the engine is decelerating. It eliminates the popping when you close the throttle. It allows a leaner main air mix in an effort to get to a lower emissions.
Anybody know what one might want to use to get started? I've got a 76 500 that I blew the engine on and have a 74 cb450 that I'm dropping in as a full replacement. I'd prefer to keep using the 500T carbs as I know they are good... the 450's would (probably) need a full rebuild.
This tool is an absolute must for anyone dealing with an engine with multiple carburetors. I've been using this style of synchronizer for years and it works great. It even has the capacity to see the differences in air flow when the engine RPM is above idle.
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IMO it would still be easier to just drill the sync ports or better yet use the CB500T carbs instead.
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