2005-2008 Honda ATV TRX500FA/FGA Fourtrax, Rubicon Factory Service Manual, Page 122Get this manual
FUEL SYSTEM Check the jet needle for stepped wearCheck the vacuum piston for wear or damageCheck the diaphragm for pin hole, deterioration or damageCheck the vacuum piston for smooth operation up and down in the carburetor bodyAir will leak out of the vacuum chamber if the diaphragm is damaged in any way, even with just pin holeJET NEEDLE DIAPHRAGMPISTON