Yamaha MX250 - Troubleshooting Guide; Engine Start and Stalling Issues

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TROUBLESHOOTING
6-1
TROUBLESHOOTING
ENGINE DOES NOT START
No. Checking steps Possible remedy
1
Check the engine oil level.
(Refer to “ENGINE OIL LEVEL” on page 2-4)
Add the oil if it is insufficient.
2 Check the fuel level. Add the fuel if it is insufficient.
3 Check if the fuel has deteriorated. Replace the fuel.
4 Check if the fuel tank cap (canister) is clogged. Clean or replace.
5 Check the fuel cock lever position. Set the fuel cock lever to “ON”.
6 Check if the fuel flows to fuel cock.
Clean or replace the fuel tank or fuel
hose.
7
Check the spark plug.
(Refer to “SPARK PLUG” on page 2-3)
Re-gap or replace the spark plug.
8
Check the ignition spark gap.
(Refer to “CHECKING THE IGNITION SPARK GAP” on
page 5-4)
If the ignition spark gap is OK, the igni-
tion system is OK.
9
Check the ignition coils.
(Refer to “CHECKING THE IGNITION COIL (TCI UNIT,
PRIMARY) RESISTANCE” on page 5-6)
Replace the ignition coil.
10
Check the spark plug cap resistance.
(Refer to “CHECKING THE SPARK PLUG CAP RESIS-
TANCE” on page 5-5)
Replace the spark plug cap.
11 Check the carburetor for clogged passages or fuel overflow. Clean.
12
Check the compression pressure.
(Refer to “MEASURING THE COMPRESSION PRES-
SURE” on page 3-1)
Too high:
Decarbonize the combustion chamber if
there is carbon deposits.
Too low:
Next checking steps.
13
Check the valve clearance.
(Refer to “ADJUSTING THE VALVE CLEARANCE” on
page 2-11)
Adjust the valve clearance.
14
Check the valve face and valve seat for wear.
(Refer to “VALVE” on page 3-26)
Resurface or replace the valve face and
valve seat.
15
Check if the marks on the crankshaft and camshaft are
aligned.
(Refer to “INSTALLING THE VALVE LIFTER AND CAM-
SHAFT” on page 3-36)
Correct.
16
Check if there is seizure, wear, or damage on the piston,
piston ring, or cylinder.
(Refer to “PISTON, CAMSHAFT, CRANKCASE, AND
CRANKSHAFT” on page 3-32)
Rebore or replace.