Yamaha YFM400FWA 2000 5GH3-AE1 Service Manual page 237

CARBURETOR
5.Inspect:
Vacuum chamber cover 1
Spring 2
Cracks/damage → Replace.
6.Inspect:
Diaphragm (coasting enricher) 1
Spring 2
Cover 3
Tears (diaphragm)/damage → Replace.
7.Inspect:
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 → Blow out the jets with com-
pressed air.
8.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.
9.Check:
Free movement (throttle valve)
Sticks → Replace.
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CARB