Symptoms

Possible cause

Resolution

Engine hard to start, idles

Breaker points dirty or out of

Clean and adjust points

poorly or runs erratically

adjustment

HT pickup and slip ring dirty (mag ignition)

Remove pickup wire, wipe clean, wipe collector

ring while rotating engine.

Magneto or ignition coil fault

Remove spark plug and check spark will jump

gap (1/8" for magneto and 1/4" for coil) when

engine is turned over. Check again when

everything is warmed up to determine whether

there is any deterioration.

Condenser fault

Usually indicated by rapid pitting of the contact

breaker points and steady intense blue spark

across the contacts, whereas a small white

spark is normal.

Ignition coil or condenser terminals loose

Check and tighten

Water in carb

Drain carb bowl, blow out jets and passage ways

Carb out of adjustment or

Adjust mixture and clean carb with suitable

requires cleaning

aerosol cleanser.

Fuel flow restricted

Check vent hole in filler cap is not blocked.

Engine misfires when

Dirty plugs

Clean plugs or replace

accelerating

Weak spark

Check ignition system

Magneto pick up brush missing

Replace

Dirty pick up or collector ring

Clean

Plug cap or HT cable faulty

Replace

Poor idle

Air leakage at carb flange

Tighten (do not over tighten as you will distort

flange). Replace gasket or rubber seal

Air leakage in manifold balance pipe

Seal joint or replace pipe.

Worn carb slide and body

Replace carb

Engine cuts out and

Dirty spark plug

Clean or replace spark plug

misfires on load

Plug gap to large

Adjust to correct size

Pronounced when climbing

Weak spark or ignition trouble

Battery ignition check coil and set points

hils

Magneto ignition clean and set points, check

armature and condenser.

Engine hesitates or dies

Blocked carb main jet

Remove main jet and blow through. Avoid using

when full throttle is applied

a pin to clear.

Water in carb

Drain and clean carb bowl, jets and passages

Mixture too weak

Raise needle position, increase main jet or adjust

as per manufacturer instruction.

Blue smoke from exhaust

Worn bore or piston rings

Replace piston rings.

when engine is warmed up

Re-bore, fit new piston and rings.

Blue smoke from exhaust

Worn valve guides or valve stems

Replace valves if the stem is worn or replace

when changing gear

both guide and valve if excessive play in the guide

Misfire in wet weather

Short circuit of HT system

Check plug cap, coil and cable. Use duck oil

(water repellant)

Blue smoke from exhaust

Worn valve stems

Replace valve and re-cut seat

when cold starting and

Worn valve guides

Replace valve and re-cut seat.

when gear changing