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Problem and possible cause Remedy
1. Ignition system problems
1) Spark plug
Improper spark plug gap
Insulation defect
Carbon deposits
Adjust the gap
Replace
Clean
2) Ignition coil
Insulation defect or discontinuity
Poor contact or broken wire
Replace
Repair or replace
3) Improper air gap between ignition coil and flywheel Adjust
2. Fuel system problems 1) No fuel in fuel tank Refill
2) Fuel hose clogged or pinched Clean or replace
3) Air in fuel lines Check and retighten joints
4) Poor quality gasoline or water in gasoline Replace
5) Carburetor
Overflow
Clogged or damaged
Throttle valve malfunction
(does not close fully)
Adjust
Overhaul
Check and adjust
3. Engine core components
problems
1) Insufficient tightening of cylinder head bolts Check and retighten
2) Wearing of piston, piston rings and/or cylinder
Repair or replace
3) Improper contact of valve and seat Repair
4) Valve sticking Repair
5) Improper valve clearance Adjust
6) Leakage from intake manifold gasket Retighten; replace gasket
7) Leakage from carburetor gasket Retighten; replace gasket
8) Insufficient tightening of spark plug Retighten
15. TROUBLESHOOTING
If the engine shows any sign of malfunction, the cause should be determined immediately and appropriate
countermeasures should be taken to prevent the problem from worsening. This section describes certain known
problems, their possible causes and appropriate countermeasures. Note, however, that the list of problems
presented here is not all. Generally speaking, since there is the possibility of multiple causes for a single problem,
please use your experience and common sense when deciding on what action to take.
15-1 ENGINE
The following three conditions must be fulfilled for satisfactory engine start.
1. The cylinder filled with a proper fuel-air mixture.
2. Good compression in the cylinder.
3. Good spark, properly timed, to ignite the mixture.
The engine cannot be started unless these three conditions are met. There are also other factors which
make engine start difficult, e.g., a heavy load on the engine when it is about to start at low speed, and a
high back pressure due to a long exhaust pipe.
Starting difficulties