Scooter Troubleshooting Guide

A great guide on finding answers to your problems


Problem: Bike refuses to start and will not fire.

Possible Causes: Solution:
Carburation Clean the carb out and ensure the jets are clear, ensure reed valves are closing fully and are not damaged.
Compression Piston and/or rings could be worn or barrel damaged, inspect and replace. Also check headgasket is sealing and spark plug is tight.
Ignition If there is no spark, replace the plug, if this doesn't work trace the problem back thought the coil, CDI, pulse coil (stator) and ignition switch.

Problem: Bike starts but runs "rough".

Possible Causes: Solution:
Carburation Check main/pilot jets are clear, check idle mixture setup and check for air leaks aroung the manifold, also inspect reeds for damage. This could also indicate theauto-choke sticking on.
Compression If the bike is down on compression, the tickover may become unpredictable and the bike will not rev cleanly.
Ignition It is possible that the plug is getting tired and breaking down or that the HT cap isnt connected properly, replace the spark plug and ensure the HT lead is secure.

Problem: Bike is slow to pull away.

Possible Causes: Solution:
Transmission Clutch springs could be too soft, therefore the clutch bites too early and drowns out the revs. Belt could be worn and slipping (usually you can feel this and it's indicated by a squeeling sound).
Compression If the bike is down on compression then it can cause simelar symptoms to heavy rollers (see Bike revs drop after seting off), this is due to gasses escaping down the side of the piston therefore power is lost, replace piston and rings.
Tyres under-inflated Check tyre pressures regularly, average scooter tyre pressure is 25-28PSI.

Problem: Bike Pulls away then revs drop.

Possible Causes: Solution:
Transmission Rollers are too heavy or clutch springs are too stiff (if bike excessively revs off the line).
Compression (See bike is slow to pull away)

Problem: Bike runs fine but makes a rumbling or grinding noise.

Possible Causes: Solution:
Main bearings Check main bearings by moving the crank up and down at either end, If there is any movement then your crank bearings will need replacing.
Incorrectly spaced variator The variator could be rubbing the transmission case, this can be caused by fitting of spacers and variator parts in the wrong order.
Loose flywheel Ususlly causes the bike to run badly.


Problem: Engine moves excessivly in relation to the chassis.

Possible Causes: Solution:
Worn or loose engine mounts There are many different types of engine mounts, however the common simalarity is that worn ones will make the engine move in ralation to the chassis, causing the bike to weave on the road. The cure is replacement engine mounts (or in the case of some aprilias, tightening the adjuster on the chassis to re-gain some tension).

Problem: Brakes are ineffective. (disc)

Possible Causes: Solution:
Pads are worn through This should never happen, but it frequently does, check that your brake pads have more than 1mm of meat left on them (I reccomend 3mm), if they are very low they may be running on metal, if this is the case you may need a new disc, in some extreme cases you can wear through the metal and damage the caliper.
Fluid is low Usually caused by excessive pad wear or fluid leak. Check pads and replenish fluid then bleed brakes.
Master cylinder seals are damaged A tough one to find but the symptoms are heavy pumping can gain a poor brake again for short period of time. Replace master cylinder (or purchase seal kit).

Problem: Brakes are ineffective. (drum)

Possible Causes: Solution:
Cable is broken or loose Try tightening adjuster (usually near the back wheel) if the cable is broken then replace.
Actuator arm is damaged This can happen if you drop down a particularly unlucky curb, the only remedy is to replace the arm.
Shoes are worn excessively Very rare for this to happen but replacement is the only answer.

Problem: Front wheel moves backwards and forwards in relation to the chassis.

Possible Causes: Solution:
Headstock bearings are worn Either try to tighten the bearings slightly (so that there is no forwards/backwards movement in the forks but the steering is still free) or replace then follow adjustment precedure.
Wheel bearings are damaged wheel will "wobble" slightly in relation to the forks, replace bearings.

Problem: Bike "crabs" on the road.

Possible Causes: Solution:
Engine mounts (See engine moves excessively in relation to chassis)
Chassis is bent/twisted It is possible for the chassis to have been bent in an accident, get it professionally checked.
Tyre wear is uneven Replace tyres.


Problem: Speedometer doesn't register my speed. (analogue)

Possible Causes: Solution:
Cable broken Replace cable.
Drive broken Replace drive.

Problem: Speedometer doesn't register my speed. (digital)

Possible Causes: Solution:
Cable disconnected Re-connect.
Reed switch or magnet in drive damaged Replace or repair speedo drive.

Problem: My indicators flash too quickly/slowly.

Possible Causes: Solution:
Wrong bulbs Check that you are using the correct wattage of bulbs (some LED indicators need resistors put into the circuit).
Dead battery Charge or replace.

Problem: Lights are dim.

Possible Causes: Solution:
Wrong bulbs Many scooters can't cope with powerful bulbs, replace with a more suitable wattage (usually 35w).
Damaged regulator Replace.

Problem: Bulbs keep blowing.

Possible Causes: Solution:
Damaged regulator unit Replace.
Damaged regulator Replace.

Problem: Fuse keeps blowing.

Possible Causes: Solution:
Direct short to earth Trace fault, commonly brake light switch or damaged wire.

Problem: Brake lights don't illuminate when lever is pulled.

Possible Causes: Solution:
Brake switch Replace.
Bulb Replace.

Problem: Electric start doesn't work or only works with one brake.

Possible Causes: Solution:
Brake switch (See Brakes don't illuminate when lever is pulled)
Relay is damaged Listen for a click when you press the starter switch.
Bad earth Run a multimeter between the positive into the motor and earth, if no voltage or very low voltage, check the earth to the engine/starter (also check battery).

Problem: No electrics work.

Possible Causes: Solution:
Check the fuse Replace if blown.
Check battery connectors Re-connect if loose.
Nov 26, 2011
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