reeds?

they are like a one way valve that lets the intake charge into the crank case... go to howstuffworks.com and search for 2 stroke engine. to check them, take them out and make sure they seal to the cage and that they are not cracked or chipped
 
fuel flows through them. Like hickskateboarder said, make sure they are against the cage and not bent back or chipped. Pull a reed back and if it snaps back against the cage fast then its good. If it slowly goes back to the cage its bad.