Yamaha YFM660RN Service Manual page 278

CARBURETORS
4.Check:
Piston valve 1
Scratches/wear/damage → Replace.
Rubber diaphragm 2
Tears → Replace.
5.Check:
Vacuum chamber cover 1
Spring 2
Cracks/damage → Replace.
6.Check:
Jet needle 1
Main jet 2
Needle jet 3
Pilot air jet 4
Pilot jet 5
Pilot screw 6
Starter jet 7
Starter plunger 8
Bends/wear/damage → Replace.
→
Blockage
compressed air.
7.Check:
Free movement (piston valve)
Sticks → Replace the piston valve guide and
the piston valve.
Insert the piston valve into the carburetor
body, and check for free movement.
8.Check:
Free movement (throttle valve)
Sticks → Replace.
7 - 6
CARB
Blow out the jets with