Help with reed valve explanation

[rickd20006]

Hey guys can someone explain to me the function of reed valves, and symptoms if not functioning properly.
Half alot of gas spitting around the throttle chamber at idle just behind the butterflys. Fuel seems to pool in that area as well.
Can they be replaced.

Thanks in advance

Rick

 

[imported_lorin]

Re: Help with reed valve explanation

They're thin sheets of metal. When a piston goes up it creates a vacuum that pulls the valve off its "seat" allowing fuel to enter the crankcase. When the piston goes down pressure forces the valve closed against its "seat" so fuel isn't forced back out through the carb. Sometimes they break-when they do so you can see fuel being spit back out the carb. The broken part gets sucked into the cylinder but often doesnt cause any damage as it gets blown out the exhaust. They're fairly easy to replace. They usually last a very long time but they can get worn out without breaking. When this happens you can have generally lousy performance.

 

[Xcusme]

Re: Help with reed valve explanation

Rick,
The reed valves act as 'one way valves'. The reeds are located in the intake manifold , just behind the carb(s). As the piston rises in the cylinder, this creates a vacuum in the crankcase. This vacuum draws fresh fuel mix, through the carb throat, past the reed valve and into the crankcase.
As the piston moves down the bore, the reeds seal the fresh fuel mix from escaping back through to the carb, and this increased crankcase pressure, forces the fuel mix up into the cylinder above the piston.
Having fuel being forced back out the front of the carb throat can indicate that the reeds are not sealing properly. Yes, the reeds and be replaced. Remove carb(s), remove intake manifold. The reeds are mounted on the crankcase side of the intake manifold.

 

[rickd20006]

Re: Help with reed valve explanation

Hey thanks guys
Is there a way to tell if they are not seating properly>

 

[imported_lorin]

Re: Help with reed valve explanation

You can remove them and hold them horizontal and you shouldn't see any space between the valve and the metal plate area where they seat. However, they could look ok but still be worn out, although again, they usually last quite a long time. They're not real easy to diagnose. It's like if everything else is ok and you still have lousy performance you might suspect the valves. If you have a small motor and you suspect problem with them maybe you should just replace them.