Here is a quick guide for you to compare your spark plugs to. Check to see if your air/fuel ratio is fine etc.
NORMAL
Light grey or tan deposits and slight electrode erosion.
CARBON FOULING
Dry, soft black carbon on the insulator and electrodes.
Symptoms:
- Misfiring
- Poor starting
- Faulty acceleration
Causes:
- Delayed ignition timing
- Faulty choke - over rich air/fuel mixture
- Bad ignition leads
- Plug heat range too cold
PRE-IGNITION
A melted or burned center and/or ground electrode, blistered insulator and aluminum or other metallic deposits on the insulator.
Symptoms:
- Pre-ignition occurs when combustion begins before the timed spark occurs
- Loss of power causing engine damage
Causes:
- Plug insufficiently tightened
- Engine insufficiently cooled
- Ignition timing too advanced
- Plug heat range too hot
OVER HEATING
An extremely white insulator with small black deposits and premature electrode erosion.
Symptoms:
- Misfiring
Causes:
- Plug nose is too long for engine head
- Foreign object (bolt/nut) in combustion chamber
OIL FOULING
Wet, oily black deposits on the insulator and electrodes.
Symptoms:
- Poor starting
- Misfiring
Causes:
- Wrong piston rings, cylinders, and valve guides
- Fuel mixture oil content too high (two-stroke engines)
BROKEN INSULATOR
Insulator is cracked or split.
Symptoms:
- Misfiring
Causes:
- Severe detonation
- Incorrect tool/torque applied during installation or removal
- Careless gap setting
TORCHED SEAT
Melted in the thread and seat area of the plug housing.
Symptoms:
- Loss of power causing engine damage
Causes:
- Plug insufficiently tightened
