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What is the purpose of the diaphram on the left side of the carb? and when it goes bad could it cause a very rich running condition ?
 

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What is the purpose of the diaphram on the left side of the carb? and when it goes bad could it cause a very rich running condition ?
I don't have the carb in front of me, but I believe the part you are referring to is part of the "coaster circuit". That's what Yamaha calls it, there may be other names for it.



It provides an extra bit of fuel when the throttle is quickly closed... that extra fuel helps prevent backfiring.



If the diaphragm is damaged, the fuel is provided continuously which could lead to a rich condition. However, the hole where this extra fuel enters the carb throat is so small, I suspect it's not a great amount of extra fuel.



jb
 

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So to eliminate this for test reasons all all need to do is pinch it off in the middle and see how it does , thanks
 
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