Symptoms

Possible cause

Resolution

Engine Fails to

Fuel Shortage

Check there is fuel in the tank

start

Blockage in carb jet or fuel line

Check fuel is flowing from the tank to the carb,

remove pipe is necessary or use tickler

No fuel in carb

Check float is not stuck or jet blocked

Carb flooded

Wet spark plug insulator is obvious sign. Kick

over the engine with the throttle wide open and

the fuel off to clear excess fuel.

Remove spark plug, clean and dry in the

sunshine or warm place.

Spark failure

Remove spark plug from cylinder head, lodge

on metal fins and kick over engine. If you do

not get a spark, change the plug. If still no

spark check: Points and condenser, you should

get a spark across the points as you open them

with a screwdriver blade. If not, check battery

and wires. Change coil.

Fouled or 'Wiskered' plug

Clean or replace plug. Two strokes suffer from

wiskering where a deposit bridges the plug gap,

a remedy is a cooler plug or larger gap.

No electrical power

Battery may be dead, on battery ignition models

is evident by no lights or horn. Check the fuse,

if fitted. Charge battery if dead. Check, clean

and tighten battery terminals.

Bump start is possible on some models,

Disconnect battery earth lead and reconnect

When started.

Slipped ignition timing

If there is a spark, check that it comes just

Before top-dead-centre.

Check timing marks if present.

Engine fails to

Wet HT leads, plug covers, ignition

Dry off these components (you can spray with

start after rain or

coil or distributor

Duck oil-water repellent)

washing

Dry off spark plugs or turn over engine with

throttle open.

Clicking noise

Tappet clearance to great

Adjust tappets to correct clearance

from engine at

higher revs

Engine runs

Stale fuel

Drain the fuel from the tank and refill with new

poorly after period

fuel

of storage

Gum deposits in carb

Clean carb with suitable aerosol carb cleanser

or metholated spirits.

Knock when

Piston slap

Check clearances on piston and bore. May need

accelerating

new piston or re-bore as well as piston.

Small end bearing

Check tolerances no more than 3 thou.

Medium speed

Mixture too rich

Drain the fuel from the tank and refill with new

misfire

Magneto fault

Check magneto for fault and repair

Coil fault

Replace coil

Engine overheating

Weak mixture

Raise needle position, increase main jet or

adjust as per manufacturer instruction.

Ignition timing out

Retime ignition to manufacturers settings.

Spark plug wrong grade

Replace with manufacturers recommended

grade or equivalent.