Chapter 9. Troubleshooting; Starting Failure/Hard Starting; Fuel System; Compression System - Yamaha YP250 Service Manual

EB90000
NOTE:
The following troubleshooting does not cover all the possible causes of trouble. It should be helpful,
however, as a guide to troubleshooting. Refer to the relative procedure in this manual for inspection,
adjustment and replacement of parts.
YP90000

STARTING FAILURE/HARD STARTING

FUEL SYSTEM

Fuel tank
D Empty
D Clogged fuel tank cap breather hole
D Deteriorated fuel or fuel containing water or
foreign material
Fuel pump
D Clogged fuel hose
D Clogged fuel pump
D Broken vacuum hose or improperly hose set-
ting
Carburetor
D Deteriorated fuel or fuel containing water or
foreign material
D Clogged pilot jet
D Clogged air passage
D Improperly set pilot air screw
D Clogged pilot air passage
D Improperly sealed valve seat
D Improperly adjusted fuel level
D Clogged starter jet
D Clogged emulsion (heated water) tube
D Sucked-in air

COMPRESSION SYSTEM

Cylinder and cylinder head
D Loose spark plug
D Loose cylinder head
D Broken cylilnder head gasket
D Broken cylinder gasket
D Worn, damaged or seized cylinder
Piston and piston ring
D Worn piston
D Worn, fatigued or broken piston ring
D Seized piston ring
D Seized or damaged piston
STARTING FAILURE/HARD STARTING
TROUBLESHOOTING
9-1
Auto choke
D Starter plunger malfunction
D Wax malfunction
D P.T.C. thermister malfunction
D Ignitor unit malfunction
D Thermo switch malfunction
Air cleaner
D Clogged air cleaner element
D Improper air cleaner setting
Valve system
D Improperly adjusted valve clearance
D Improperly sealed valve
D Improperly contacted valve and valve seat
D Improper valve timing
D Broken valve spring
D Seized valve
TRBL
SHTG