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REF04
Fault finding
2 Poor running at low speeds (continued)
Compre~~ion
/OW
Cylinder head gasket damaged. If a head is allowed to become
Spark plug loose. Remove the plug and inspect its threads
(Chapter 1).
Cylinder head not sufficiently tightened down. If the cylinder head
is suspected of being loose, then there's a chance that the gasket
or head is damaged if the problem has persisted for any length of
time. The head bolts should be tightened to the proper torque in
the correct sequence (Chapter 2).
Low crankcase compression due to wom crankshaft oil seals.
Condition will upset the fueVair mixture. Renew the seals (Chapter 2).
Cylinder and/or piston worn. Excessive wear will cause
compression pressure to leak past the rings. This is usually
accompanied by worn rings as well. A top-end overhaul is
necessary (Chapter 2).
Piston rings worn, weak, broken, or sticking. Broken or sticking
piston rings usually indicate a lubrication or carburation problem
that causes excess carbon deposits to form on the pistons and
rings. Top-end overhaul is necessary (Chapter 2).
Piston ring-to-groove clearance excessive. This is caused by
excessive wear of the piston ring lands. Piston renewal is
necessary (Chapter 2).
loose, or if excessive carbon build-up on the piston crown and
combustion chamber causes extremely high compression, the
head gasket may leak. Renew the gasket (Chapter 2).
Cylinder head warped. This is caused by overheating or
improperly tightened head bolts. Machine shop resurfacing or
head renewal is necessary (Chapter 2).
Poor acceleration
Carburettor leaking or dirty. Overhaul the carburettor (Chapter 4).
Faulty automatic choke (Chapter4).
Timing not advancing. The pulse generator coil or the CDI unit
may be defective (Chapter 5). If so, they must be replaced with
new ones, as they can't be repaired.
Brakes dragging. On disc brakes, usually caused by debris which
has entered the brake piston seals, or from a warped disc or bent
axle. On drum brakes, cable out of adjustment, shoe retum spring
broken. Repair as necessary (Chapter 8).
Clutch slipping, drive belt worn, or speed governor faulty
(Chapter 2C).
3 Poor running or no power at high speed
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Firing incorrect
Air filter clogged. Clean filter (Chapter 1).
Spark plug fouled, defective or worn out. See Chapter 1 for spark
plug maintenance.
Spark plug cap or HT wiring defective. See Chapters 1 and 5 for
details of the ignition system.
Spark plug cap not in good contact (Chapter 5).
lncorrect spark plug. Wrong type, heat range or cap configuration.
Check and install correct plug listed in Chapter 1.
CDI unit or HT coil defective (Chapter 5).
Fuel/air mixture incorrect
Main jet clogged. Dirt, water or other contaminants can clog the
main jet. Clean the fuel tap filter and the carburettor (Chapter 4).
Main jet wrong size. The standard jetting is for sea level
atmospheric pressure and oxygen content.
Air bleed holes clogged. Remove and overhaul carburettor
(Chapter 4).
Air filter clogged, poorly sealed, or missing (Chapter 1).
Air filter housing or duct poorly sealed. Look for cracks, holes or
loose clamps or screws, and replace or repair defective parts.
Carburettor inlet manifold loose. Check for cracks, breaks,
damaged gaskets or loose clamps.
Compression low
Spark plug loose. Remove the plug and inspect its threads.
Reinstall and tighten securely (Chapter 1).
Cylinder head not sufficiently tightened down. If the cylinder head
is suspected of being loose, then there's a chance that the gasket
or head is damaged if the problem has persisted for any length of
time. The head bolts should be tightened to the proper torque in
the correct sequence (Chapter 2).
Low crankcase compression due to worn crankshaft oil seals.
Condiiion will upset the fueVair mixture. Renew the seals (Chapter 2).
Cylinder and/or piston worn. Excessive wear will cause
compression pressure to leak past the rings. This is usually
accompanied by worn rings as well. A top-end overhaul is
necessary (Chapter 2).
Piston rings worn, weak, broken, or sticking. Broken or sticking
piston rings usually indicate a lubrication or carburation problem
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that causes excess carbon deposits to form on the pistons and
rings. Top-end overhaul is necessary (Chapter 2).
Piston ring-to-groove clearance excessive. This is caused by
excessive wear of the piston ring lands. Piston renewal is
necessary (Chapter 2).
Cylinder head gasket damaged. If a head is allowed to become
loose, or if excessive carbon build-up on the piston crown and
combustion chamber causes extremely high compression, the
head gasket may leak. Renew the gasket (Chapter 2).
Cylinder head warped. This is caused by overheating or
improperly tightened head bolts. Cylinder head skimming or head
renewal is necessary (Chapter 2).
Knocking or pinking
Carbon build-up in combustion chamber. Use of a fuel additive
that will dissolve the adhesive bonding the carbon particles to the
crown and chamber is the easiest way to remove the build-up.
Otherwise, the cylinder head will have to be removed and
decarbonised (Chapter 1).
lncorrect or poor quality fuel. Old or improper grades of fuel can
cause detonation. This causes the piston to rattle, thus the
knocking or pinking sound. Drain the old fuel and refill with fresh
fuel of the recommended grade (Chapter 4).
Spark plug heat range incorrect. Uncontrolled detonation indicates
the plug heat range is too hot. The plug in effect becomes a glow
plug, raising cylinder temperatures. Install the proper heat range
plug (Chapter 1).
Improper aidfuel mixture. This will cause the cylinder to run hot,
which leads to detonation. Clogged carburettor jets or an air leak
can cause this imbalance. See Chapter 4.
Miscellaneous causes
Throttle valve doesn't open fully. Adjust the throttle twistgrip
freeplay (Chapter 1).
Clutch slipping, drive belt worn, or speed governor faulty
(Chapter 2C).
Brakes dragging. On disc brakes, usually caused by debris which
has entered the brake piston seals, or from a warped disc or bent
axle. On drum brakes, cable out of adjustment, shoe return spring
broken. Repair as necessary (Chapter 8).
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