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Discussion Starter #1
Anyone know what the purpose of the air cut off valve is? It's that small, spring loaded diaphragm at the top of the carbs on the 650's.
 

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That diaphram pulls the needle out of the main jet to richen up the mixture as the motor needs it.It is controlled by vacuum so the motor only gets what it needs.Varying load changes vacuum which chages rate at whic the needle is pulled up.
 

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That diaphram pulls the needle out of the main jet to richen up the mixture as the motor needs it.It is controlled by vacuum so the motor only gets what it needs.Varying load changes vacuum which chages rate at whic the needle is pulled up.
Wrong diaphragm, your talking about the throttle diaphragm

CUT OFF VALVES PREVENT "AFTER BURN" GENERATED WHEN THE THROTTLE IS SUDDENLY CLOSED WHEN THE THROTTLE IS SUDDENLY CLOSED, THE VALVE TEMPORARILY CLOSES THE SLOW-JET PASSAGEWAY---CREATING AN INSTANTLY RICHER MIXTURE AND THUS REDUCES "POP" SOUNDS UPON DE-ACCELERATION
 

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Discussion Starter #4
Thanks, Hunterworks. I noticed that one of the air cut off valves on my bike was in pretty bad shape, but didn't have time to replace it before my next ride. During that ride, I noticed more "pop" when backing off of the throttle and was concerned about my engine brake.
 

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i always wondered why these things dont pop on deceleration. i wish mine popped more, i love that sound
 

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The air cut off closed one of the pilot air passages so more fuel in drawn into the cylinder on deceleration. I changed mine as i thought it was the cause of backfiring on decel.
 

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