1988-1994 Honda TRX300 Fourtrax, 1988, 1990-1994 TRX300FW Fourtrax Service Manual, Page 60Get this manual
FUEL SYSTEM Remove the compression spring and diaphragmvacuum pistonInspect the vacuum piston for wear, nicks, or ther damageMake sure the piston moves up and down freely in the chamberSPRING
Push the jet needle holder down and turn it counterclockwise 90 degrees with an mm socketThen remove the needle holder, jet needle and washer from the diaphragmvacuum piston