Fault Finding

Starter motor does not rotate

 * Engine stop switch OFF.
 * Fuse blown. Check main fuse.
 * Battery voltage low. Check and recharge battery
 * Faulty clutch switch, neutral switch or side-stand switch. Check the wiring to the switch and the switch itself.
 * Starter motor defective. Make sure that the wiring to the starter is clean and secure. In addition, make sure the starter relay clicks when the start button is pushed. If the relay clicks, the fault is in the wiring or motor. Check the starter motor brushes.
 * Starter relay or starter circuit relay faulty.
 * Starter button not contacting. Are the contacts wet, corroded or dirty? Disassemble and connect the switch.
 * Wiring open or shorted. Check all the wiring connections and harnesses to make sure they are tight and dry. Make sure they are not corroded. Also check for broken or frayed wires that could cause a short to ground.
 * Ignition switch defective. Check the switch.
 * Engine stop switch defective. Again, check if the switch has wet, dirty or corrosion on the contacts. Clean or replace as necessary.

Starter motor rotates but engine does not turn over

 * Energy conserving oil used. Causes starter clutch to slip. Change oil to approved oil.
 * Starter motor clutch defective. Inspect and repair or replace
 * Damaged idler or starter gears

Starter works but engine will not turn over

 * Seized engine possibly caused by one or more internally damaged parts. Failure possible due to wear, abuse or lack of lubrication. Damage can include seized valves, lifers, camshafts, pistons, crank, rod bearings or transmission gears or bearings.

No Fuel Flow

 * Out of fuel.
 * Petcock vacuum hose broken or disconnected
 * Clogged tank vent. Usually caused by dirt or water. Remove gas cap and clean the cap vent hole- it is the cone-shaped protrusion on the underside of the lid.
 * Petcock clogged. Remove and clean it and the screen filter.
 * Fuel line clogged. Remove the fuel line and carefully blow through it.
 * Carburetor needle valves clogged. For both valves to be clogged, either a very bad batch of fuel with unusual additives has been used, or some foreign object has entered the tank. After a machine is stored for many months without running, the fuel turns to varnish and forms deposits on the needles and jets. Carburetors should be removed and overhauled if draining the float does not solve the problem.

Engine flooded

 * Float level too high
 * Fuel valve needle worn or stuck open. A piece of dirt, rust or other debris can cause the float needle to seat improperly causing excess fuel to be admitted to the float bowl. It is VERY common for a piece of rubber fuel hose to be sheared off when the hose is connected to the petcock. This piece of rubber finds its way down into the carburetors and jams the float valve open. In this case the float bowl should be cleaned, and the needle and seat should be inspected. If the needle or seat are worn the leaking will persist and the parts should be renewed. The needles are replaceable, however the seats are pressed into the carb body, and not serviceable.
 * Starting procedure incorrect. Under normal circumstances the machine should start with no throttle. When the engine is cold the choke should be used and the engine started without opening the throttle. If the engine is flooded, turn the petcock off and hold the throttle open while cranking the engine. This will allow additional air to reach the cylinders. Don't forget to turn the petcock back on after the engine starts.

No spark or weak spark

 * Ignition switch turned off
 * Engine stop switch turned off
 * Ignition fuse blown. Check fuse
 * Battery voltage low, check and recharge as necessary
 * Spark plugs dirty, defective or worn out. Locate reason for fouled plug using plug condition chart and repair accordingly.
 * Spark plug cap or lead faulty. Check condition. Clean the inside of the cap. Trim a very small amount off of the lead and reattach the cap. If cracks or deterioration are evident, replace the parts.
 * Spark plug cap not making good contact. Make sure the cap fits snugly over the plug.
 * Pickup coil defective
 * Ignition coil defective
 * Ignition or stop switch shorted. Usually caused by water, damage or excessive wear. Switches can be disassembled and cleaned. if cleaning does not help, replace.
 * Wiring shorted or broken:
 * Between ignition switch and engine stop switch
 * IC igniter and engine stop switch
 * IC igniter and ignition coil
 * Coil and plug
 * IC igniter and pickup coil


 * Make sure all wiring connections are clean, dry and tight. Look for frayed or broken wires.
 * IC igniter defective.

Compression low

 * Spark plugs loose
 * Cylinder head not sufficiently tightened. If the cylinder head is suspected of being loose, there is a chance the gasket or head is damaged if the problem has persisted. Head bolts should be tightened to the proper torque in the correct sequence.
 * Improper valve clearance. The valve is not closing completely and pressure is leaking past the valve. Check and adjust valve clearance.
 * Cylinder or piston or rings worn. A lot of wear will case pressure to leak past the rings. Top end overhaul.
 * Head gasket damaged. If the head is allowed to become loose, or excessive carbon build up on piston chamber causes extremely high compression, the gasket may leak. Re-torquing the head may not be enough.
 * Head warped. Caused by overheating or improperly tightened head bolts. Machine shop resurfacing or head replacement is required.
 * Valve spring broken or weak.
 * Valve not seating properly.

Stalls after starting or runs only on choke

 * Carburetor malfunction. Clean carbs. Pay special attention to pilot jets.
 * Improper choke action. Make sure the choke linkage is getting full stroke and staying out.
 * Ignition malfunction
 * Fuel contaminated
 * Intake leak
 * Idle speed incorrect

Rough Idle

 * Ignition malfunction
 * Idle speed incorrect
 * Carburetors not synchronized
 * Carburetor malfunction
 * Intake air leak
 * Air filter clogged

Spark Weak

 * Battery voltage low, check and recharge as necessary
 * Spark plug incorrect. Wrong type, heat range or cap configuration.
 * Spark plugs dirty, defective or worn out. Locate reason for fouled plug using plug condition chart and repair accordingly.
 * Spark plug cap or lead faulty. Check condition. Clean the inside of the cap. Trim a very small amount off of the lead and reattach the cap. If cracks or deterioration are evident, replace the parts.
 * Spark plug cap not making good contact. Make sure the cap fits snugly over the plug.
 * Pickup coil defective
 * Ignition coil defective
 * IC Igniter defective

Fuel/air mixture incorrect

 * Pilot screws out of adjustment
 * Pilot jet or air passage clogged
 * Air bleed holes clogged
 * Air filter dirty
 * Air-box to carburetor connections poorly seated.
 * Fuel level too high or low. Adjust floats
 * Tank vent obstructed.
 * Intake manifolds loose. check for cracks, breaks, tears or loose clamps.
 * Check both carburetor diaphragm for rips and tears.

Compression low

 * Spark plugs loose
 * Cylinder head not sufficiently tightened. If the cylinder head is suspected of being loose, there is a chance the gasket or head is damaged if the problem has persisted. Head bolts should be tightened to the proper torque in the correct sequence.
 * Improper valve clearance. The valve is not closing completely and pressure is leaking past the valve. Check and adjust valve clearance.
 * Cylinder or piston or rings worn. A lot of wear will case pressure to leak past the rings. Top end overhaul.
 * Head gasket damaged. If the head is allowed to become loose, or excessive carbon build up on piston chamber causes extremely high compression, the gasket may leak. Re-torquing the head may not be enough.
 * Head warped. Caused by overheating or improperly tightened head bolts. Machine shop resurfacing or head replacement is required.
 * Valve spring broken or weak.
 * Valve not seating properly.

Poor acceleration
- Missed idle; sometimes work only one cylinder. - Sand or dirt in bottom part - jet's clogged, dirt under level needle; tugs and stops on low rpm, idle present. - Thin small sand under valve vacuum membrane; it can't move smoothly.
 * Carbs leaking or dirty.
 * Wrong fuel mixture - check screw-pilot turns.
 * Timing not advancing. The pick up coil unit or IC igniter may be defective. If so, they must be renewed, as they can not be serviced.
 * Carbs not synchronized.
 * Engine oil viscosity too high. Using heavier than recommended can damage the oil pump or lubrication system and cause drag on the engine
 * Brakes dragging. Usually caused by debris which has entered the piston boot or from a warped disc.

Firing incorrect

 * Air filter dirty
 * Plugs fouled
 * Plug cap or lead defective
 * Plug cap not in good contact
 * Incorrect plug, wrong type, heat range or cap.
 * Ignition coils defective
 * IC Igniter defective

Fuel/Air mixture incorrect

 * Main jet clogged
 * Main jet wrong size. Standard jetting is for sea level pressure and oxygen content
 * Throttle shaft to carburetor body clearance excessive
 * Air bleed holes clogged. Remove and overhaul carbs
 * Fuel level too high or low. Adjust floats
 * Tank vent obstructed. Make sure the vent is clear
 * Fuel line clogged.
 * Restricted (on some European models) or damaged diaphragm

Compression low

 * Spark plugs loose
 * Cylinder head not sufficiently tightened. If the cylinder head is suspected of being loose, there is a chance the gasket or head is damaged if the problem has persisted. Head bolts should be tightened to the proper torque in the correct sequence.
 * Improper valve clearance. The valve is not closing completely and pressure is leaking past the valve. Check and adjust valve clearance.
 * Cylinder or piston or rings worn. A lot of wear will case pressure to leak past the rings. Top end overhaul.
 * Head gasket damaged. If the head is allowed to become loose, or excessive carbon build up on piston chamber causes extremely high compression, the gasket may leak. Re-torquing the head may not be enough.
 * Head warped. Caused by overheating or improperly tightened head bolts. Machine shop resurfacing or head replacement is required.
 * Valve spring broken or weak.
 * Valve not seating properly.

Knocking or pinging

 * Carbon build up in combustion chamber. Using a fuel additive that will dissolve the carbon bonds is the easiest way to remove build up. Otherwise, the head will have to be removed and cleaned.
 * Incorrect or poor quality fuel. Old or improper grade gasoline can cause detonation. This causes the piston to rattle, thus the knocking sound. Drain old fuel and replace with proper fuel.
 * Spark plug heat range incorrect. Uncontrolled detonation indicates the plug heat range is too hot. The plug effectively becomes a glow plug, raising cylinder temperature. Install the proper heat range plug.
 * Improper air/fuel mix. Will cause the cylinder to run hot, which leads to detonation. Clogged jets or possibly an air leak can cause this.

Miscellaneous causes

 * Throttle valve does not open fully. Adjust the cable slack.
 * Clutch slipping. Caused by improper adjustment of the cable or cable damaged or snagging on something.
 * Timing not advancing
 * Oil viscosity too high. Using a heaver oil can damage the oil pump, passages and/or cause drag on the engine.
 * Brakes dragging. Usually caused by debris which has entered the piston boot or from a warped disc (or sticking operating cam on drums).

Cooling system not operating properly

 * Coolant low
 * Leak in coolant system. Check hoses and radiator for leaks/damage. Replace or repair as necessary.
 * Thermostat sticking open.
 * Faulty radiator cap. Remove the cap and have it pressure tested.
 * Coolant passages clogged. Drain and flush the system, then refill with new coolant
 * Water pump defective. repair/replace
 * Clogged radiator fins. Clean them with compressed air, blowing from the back side.

Firing incorrect

 * Plugs fouled
 * Incorrect plug or heat range
 * Faulty ignition coils.

Fuel/Air mixture incorrect

 * Main jet clogged
 * Main jet wrong size. Standard jetting is for sea level pressure and oxygen content
 * Throttle shaft to carburetor body clearance excessive
 * Air bleed holes clogged. Remove and overhaul carbs
 * Fuel level too high or low. Adjust floats
 * Tank vent obstructed. Make sure the vent is clear
 * Fuel line clogged.
 * Intake manifolds loose or cracked. Replace or repair.

Compression too high

 * Carbon build up in combustion chamber
 * Improperly machined head surfaces, or installation of incorrect head gasket.

Engine load excessive

 * Clutch slipping. Caused by improper adjustment, snagging or damage.
 * Too much engine oil. Too much oil will cause pressurization of the crankcase and inefficient operation. Check oil and drain to proper level. If oil smells like gasoline, repair carburetor and petcock also.
 * Oil viscosity too high
 * Brakes dragging

Lubrication inadequate

 * Not enough oil. Oil provides a definite cooling function in the engine. Check oil.
 * Poor quality oil, or incorrect viscosity or type.

Clutch slipping

 * No clutch lever play. Adjust free play.
 * Friction plates worn or warped. Overhaul clutch.
 * Steel plates worn or warped.
 * Clutch springs broken or weak.
 * Clutch release not adjusted properly
 * Clutch inner cable hanging up. Caused by frayed cable or kinked outer cable. Replace the cable. Repair of a frayed cable is not advised.
 * Clutch release mechanism defective. Check the shaft, cam, actuating arm and pivot.
 * Clutch hub or housing worn unevenly. This causes improper engagement of the discs. Renew the parts.

Clutch not disengaging completely

 * Free play excessive. Adjust at bars or at engine
 * Clutch plates warped or damaged. Causes clutch to drag which causes the machine to creep. Overhaul clutch
 * Spring tension uneven. Caused by weak or broken spring. Check and renew.
 * Engine oil deteriorated. Old worn out oil will not provide proper lubrication for the clutch, causing drag. Change oil and filter.
 * Old viscosity too high.
 * Clutch housing seized on shaft. Lack of lubrication, severe wear or damage can cause the housing to seize. Overhaul of clutch and possibly transmission may be necessary.
 * Clutch release mechanism defective.
 * Loose clutch hub nut.

Doesn't go into gear or lever doesn't return

 * Clutch not disengaging
 * Selector forks bent or seized. Often caused by dropping the bike, or from lack of maintenance. Overhaul transmission
 * Gears stuck on shaft. Caused by lack of lubrication or excessive wear in bearings and bushings. Overhaul transmission
 * Selector drum binding. Caused by lubrication failure or excessive wear. Renew the drums and bearings.
 * Gear-change lever return spring weak or broke.
 * Gear-change lever broken. Splines stripped out of lever or shaft, or from a drop.
 * Gear-change mechanism arm ends broken or worn. Full engagement of gears difficult. Renew shaft assembly.
 * Gear-change arm spring broken. The arm "floats" and causes sporadic operation. Renew spring

Jumps out of gear

 * Selector forks worn
 * Gear grooves worn
 * Gear dogs or slots worn or damaged. Call FOG

Over-selection

 * Selector drum gear positioning lever not functioning or spring is broken.

Knocking or pinging

 * Carbon build up in combustion chamber. Using a fuel additive that will dissolve the carbon bonds is the easiest way to remove build up. Otherwise, the head will have to be removed and cleaned.
 * Incorrect or poor quality fuel. Old or improper grade gasoline can cause detonation. This causes the piston to rattle, thus the knocking sound. Drain old fuel and replace with proper fuel.
 * Spark plug heat range incorrect. Uncontrolled detonation indicates the plug heat range is too hot. The plug effectively becomes a glow plug, raising cylinder temperature. Install the proper heat range plug.
 * Improper air/fuel mix. Will cause the cylinder to run hot, which leads to detonation. Clogged jets or possibly an air leak can cause this.

Piston slap or rattling

 * Cylinder to piston clearance excessive
 * Bent rod. Caused by over revving, starting a flooded engine, ingesting a foreign object, etc.
 * Pin or pin bore worn
 * Rings worn/broken
 * Piston seizure damage
 * Rod bearing or piston pin end clearance excessive.
 * Caused by lack of lubrication, excessive wear

Valve noise

 * Incorrect valve clearance.
 * Valve spring broken or weak.
 * Camshaft or cylinder head worn or damaged. Lack of lubrication at high RPM is a cause of damage. Not enough oil or failure to change the oil are main causes. There are no replaceable bearings in the head, so the head itself will have to be renewed if there is excessive wear or damage.

Other noise

 * Head gasket leaking
 * Exhaust pipe leaking at cylinder head. Caused by improper fit of pipes or loose flange.
 * Crankshaft run-out excessive. Bent crank (from over-revving) or damage from other component failure.
 * Engine mounts loose.
 * Crank bearings worn
 * Cam chain tensioner defective.
 * Cam chain, guide or sprockets worn
 * Loose alternator rotor.

Clutch noise

 * Clutch housing/friction plate excessive clearance
 * Loose or damaged pressure plate and/or bolts.

Transmission noise

 * Bearings worn. Also possible shafts worn too. Call FOG.
 * Gears worn or chipped.
 * Metal chips stuck in gear teeth. possible pieces from a broken clutch, gear or selector that were picked up by the gears. Will cause early bearing failure.
 * Not enough oil. Causes a howl from transmission. Also affects engine power and clutch operation.

Chain noise

 * Chain not adjusted properly
 * Sprocket loose.
 * Sprocket worn.
 * Wheel coupling worn. Renew rubber damper.

Front end noise

 * Low fluid level or improper viscosity in forks. Can sounds like spurting and is usually coupled with irregular fork action.
 * Spring weak or broken. Makes a clicking or scraping sound. Fork oil will have lots of metal in it.
 * Steering head bearing loose or damaged. Clicks when braking.
 * Fork clamps loose
 * Fork tube bent. High probability if the bike has been dropped.
 * Axle or clamp bolt loose.

Shock absorber noise

 * Fluid level incorrect. Indicates a leak caused by defective seal. Shock will be covered in oil.
 * Defective shock absorber with internal damage. This is in the body of the shock and can not be remedied. The shock must be replaced.
 * Bent or damaged shock body.

Brake disc noise

 * Squeal caused by pats not installed or positioned correctly
 * Squeal caused by dust on brake pads. Found in combination with glazed pads. Clean using brake cleaner solvent.
 * Contaminated brake pads. Oil, brake fluid or dirt causing brake chatter. Clean or renew pads.
 * Pads glazed. Excessive heat from prolonged use or from contamination. Do not use any abrasive to roughen the pad surface, as these will stay in the pad and damage the disk. A very fine flat file can be used, but pad replacement is strongly suggested.
 * Warped disc. causes chattering, clicking or intermittent squeal. Accompanied by pulsating lever and uneven braking.
 * Loose or worn wheel bearings.

Brake drum noise

 * Shoe linings worn or contaminated.
 * Shoe linings warped or worn unevenly.
 * Brake drum out of round.
 * Loose or worn wheel bearings.

Engine lubrication system

 * Engine oil level low.
 * Engine oil viscosity too low.
 * Engine oil pump defective.
 * Camshaft or journals worn.
 * Crank or bearings worn.

Electrical system

 * Oil pressure switch defective.
 * Light circuit defective.

White

 * Piston oil ring worn.
 * Cylinders worn.
 * Valve oil seal damaged.
 * Valve guide worn.
 * Too much oil.
 * Head gasket broken between oil return and cylinder.
 * Abnormal crankcase pressurization.

Black

 * Air cleaner clogged.
 * Main jet too large or loose.
 * Choke stuck.
 * Float level too high.
 * Inlet needle held off of seat. Clean carbs.

Brown

 * Lean condition.
 * Main jet too small or clogged.
 * Fuel flow insufficient.
 * Carburetor inlet manifolds loose.
 * Air cleaner poor seal or not installed.

Handlebars hard to turn

 * Front tire pressure low.
 * Steering stem bearing adjuster nut too tight.
 * Bearings damaged. You can feel roughness as you turn the bars side to side.
 * Races dented or worn out. Denting can occur from dropping the bike or impact with an immovable object or a hole.
 * Steering stem lubrication inadequate. Repack bearings.
 * Steering stem bent. Can happen from dropping the bike or from hitting a curb or hole. Do not try to straighten the stem.

Handlebars shake or vibrate excessively

 * Tires worn or are out of balance or alignment.
 * Swing-arm bearings worn.
 * Rim damaged.
 * Wheel bearings worn.
 * Handlebar bolts loose.
 * Steering stem or fork clamps loose.
 * Engine mounting bolts loose.

Handlebars pull to one side

 * Wheels out of alignment.
 * Swing-arm bent or twisted.
 * Frame bent.
 * Steering stem bent.
 * Forks bent.
 * Fork oil level uneven.

Poor shock absorbing qualities

 * Too hard
 * Tire pressure too high.
 * Fork oil level excessive.
 * Fork oil viscosity too high.
 * Fork tube bent.
 * Fork internal damage.
 * Shock shaft or body bent or damaged.
 * Shock internal damage.
 * Too Soft
 * Fork or shock oil insufficient or leaking.
 * Fork oil too low.
 * Fork oil too light.
 * Springs weak or broken.

Brakes are spongy, don't hold (disc)

 * Air in brake line. Bleed brakes.
 * Pads or discs worn.
 * Brake fluid low or leaking.
 * Contaminated pads.
 * Master cylinder parts worn or damaged.
 * Master cylinder bore scratched from foreign material.
 * Disc warped.

Brake lever pulsates (disc)

 * Disc warped.
 * Axle bent.
 * Caliper bolts loose.
 * Caliper shafts damaged or sticking, causing caliper to bind.
 * Wheel damaged.
 * Wheel bearings damaged or worn.

Brake pedal pulsates (drum)

 * Drum out of round.
 * Wheel bearings.

Brakes drag (disc)

 * Master cylinder piston seized.
 * Lever stuck.
 * Caliper binding from inadequate lubrication.
 * Caliper piston seized in bore.
 * Pad damaged.
 * Pads improperly installed.

Brakes drag (drum)

 * Pedal free-play insufficient.
 * Springs weak or broken.
 * Operating cam stuck due to lack of lubrication.

Battery dead or weak

 * Battery faulty.
 * Poor contact.
 * Excessive load.
 * Ignition switch defective.
 * Regulator Rectifier defective.
 * Alternator stator-coil open or shorted.
 * Wiring faulty.

Battery overcharged

 * Regulator Rectifier defective. Overcharging is evident by the battery getting warm or boiling over.
 * Battery defective.
 * Amperage too low, wrong type or size.