Motorcycle Trouble shooting Guide

Our guide to common problems and possible causes

Will not start or difficult to start

If the bike won't start or is difficult to start this could be caused by a fault in the ignition system, air/fuel system or the engine/exhaust system.

Work systematically through the possible causes in the table below eliminating or fixing them as you go.


Possible causes - ignition system

No Spark - Check ignition main fuse & switch
- Check engine stop/kill switch and side stand switch if fitted
- Check Capacitor Discharge Ignition (CDI) unit if fitted
- Check magneto pick-up/charge coil and points
- Check wiring, magneto coil
- Check ignition coil
- Check HT leads
- Check spark plugs
Possible causes - air/fuel system

No Fuel - Check fuel tank
- Check fuel tap position/operation
- Remove fuel pipe - check flow to carb/pump
Intermittent or poor fuel flow - Clean fuel tank & check vent cap
- Check for blocked tank fuel filter
- Clean fuel tap & sediment bowl
- Remove & clean carburettor
Contaminated Fuel - Flush fuel system & add fresh fuel
Blocked air intake - Clean air filter
- Check reed valve assembly
Possible causes - Engine/exhaust system

Incorrect Compression Pressure - If compression too high, check excessive carbon build up
- If compression too low check:
    - cylinder head gasket
    - cylinder base gasket
    - piston, rings, cylinder
Poor bottom end compression - Check crankcase seals
Blocked Exhaust System - Check muffler/spark arrester
- Check exhaust port for carbon
- Check exhaust for damage


Poor idle/poor low speed performance

Poor idling and/or poor performance at low speeds could be the result of a problem in the ignition system or in the air/fuel system.

Work systematically through the possible causes in the table below eliminating of fixing them as you go.


Possible causes - ignition system

Spark plug fouled or incorrect gap - Clean and gap - or replace
Ignition timing incorrect - Check magneto flywheel timing marks
- Check Capacitor Discharge Ignition (CDI) unit
Weak Spark - Check ignition coil & condensor
Possible causes - air/fuel system

Tank Vent Blocked - Clean or repair as required
Fuel Tap Blocked - Clean or repair as required
Carb Idle Screw out of Adjustment - Clean and adjust
Pilot Screw out of Adjustment - Clean and adjust
Carb float level incorrect - Measure & adjust
Choke lever on - Turn lever off
Air Leak - Check & repair
Carburettor not level - Adjust


Poor mid-range/high-speed performance

Poor performance on the mid-range or at high speeds could be the result of a problem in the ignition system or in the air/fuel system.

Work systematically through the possible causes in the table below eliminating or fixing them as you go.


Possible causes - ignition system

Spark plug gap incorrect - Clean, gap or replace
Ignition incorrect - Check and reset
Timing incorrect - Check magneto flywheel timing marks
- Check Capacitor Discharge Ignition (CDI) unit
Possible causes - air/fuel system

Dirty air filter element - Clean, or replace
Carburettor float level incorrect - Measure float height & adjust if required
Incorrect main jet size - Remove jet & check size
Incorrect needle jet clip position - Check position of clip
Cracked or leaking reeds on reed valve - Remove & repair as required
Carburettor not level - Level carburettor

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9 November 2010