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Purpose of the Reed Valves

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Yeap, I'm new to the 2 stroke engines.

Just purchased a ZY80 (yr 2000) for my son.

I was hoping you could give a brief explanation of the reed valve purpose, and performance inidicators of a reed valve gone bad.

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The reed valve opens when the fuel/air mix go into the crankcase during a period of negative pressure and closes when the positive pressure in the crank tries to force the mixture back through the intake.

If your reeds are chipped it will be hard to start the bike and it will run rich pretty rich. Try to replace your reeds soon if that is the case because they have a chance of breaking off and causing further damage. reeds usually chip on the corners.

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Basic two stroke operating principle:

-As the piston moves up, there is a low pressure area created in the crank case.

-This draws air in through the carb/mixing it with fuel.

-The air flows from the carb, through the reed valve into the crank case.

-The piston, pushed down by combustion creates pressure in the crank case.

-This pressure is sealed up by the reed valve. It's a one way valve for air/fuel.

-The pressure continues to build until the piston comes down far enough to open

the transfer ports (two on each side of the cylinder).

-The pressure pushes the air/fuel up out of the crank case through the transfers

into the combustion chamber.

-Piston moves up, and it all starts again.

Bad reed valves will cause your engine to run poorly, start poorly, etc.

The only way to check them is to pull them out. If the flat reed petals don't sit tight against the reed block they should be replaced. You shouldn't be able to see a gap between the reeds and the reed block. If the edges are fraying or chipped or cracked, you need new reeds. Petals cost around $30-75. Complete assemblies like V-Force are around $120-150

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The reed valve was for produced by Yamaha . I think its a boyesen design licensed.

Before them, the charge woudl be drawn in, but much would escape backwards to the carb..nothing to hold it in. Yamaha called "their" new valve "torque induction"

Good stuff and it revolutionized the two stroke motor.

WAY more important than cartridge forks, powervalves, and about any other part you can think of.

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The reed valve was for produced by Yamaha . I think its a boyesen design licensed.

Before them, the charge woudl be drawn in, but much would escape backwards to the carb..nothing to hold it in. Yamaha called "their" new valve "torque induction"

Good stuff and it revolutionized the two stroke motor.

WAY more important than cartridge forks, powervalves, and about any other part you can think of.

Always amaze me with good info that not many of our fellow "average" people would know! :thumbsup:

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