Tune-Up Trouble Shooting: Notes
| CONDITION | POSSIBLE CAUSE | CORRECTION |
|---|---|---|
| SPARK PLUG DIAGNOSIS | ||
| Normal Spark Plug Condition | Light Tan or Gray deposits on insulator Electrode not burned or fouled Gap tolerance not changed | |
| Cold Fouling or Carbon Deposits | Over-rich air/fuel mixture Faulty choke Clogged air filter Incorrect idle speed or dirty carburetor Faulty Ignition wiring Prolonged operation at idle Sticking valves or worn valve guide seals | Adjust air/fuel mixture, see TUNE-UP Replace choke assembly, see FUEL Clean and/or replace air filter Reset idle speed and/or clean carburetor Replace ignition wiring Shut engine off during long idle Check valve train, see ENGINES |
| Wet Fouling or Oil Deposits | Worn rings and pistons Excessive cylinder wear Worn or loose bearings | Install new rings and pistons, see ENGINES Rebore or replace block Tighten or replace bearings, see ENGINES |
| Gap Bridged | Deposits in combustion chamber becoming fused to electrode | Clean combustion chamber of deposits |
| Blistered Electrode | Engine overheating Wrong type of fuel Loose spark plugs Over-advanced ignition timing | Check cooling system, see COOLING Replace with correct fuel Re-tighten spark plugs Reset ignition timing, see TUNE-UP |
| Pre-Ignition or Melted Electrodes | Incorrect type of fuel Incorrect ignition timing Burned valves Engine overheating Wrong type of spark plug, too hot | Replace with correct fuel Reset ignition timing, see TUNE-UP Replace valves, see ENGINES Check cooling system, see COOLING Replace with correct spark plug, see TUNE-UP |
| Chipped Insulators | Severe detonation Improper gapping procedure |
Check for over-advanced timing or combustion chamber deposits Re-gap spark plugs |
| Rust Colored Deposits | Additives in unleaded fuel Water in combustion chamber | Try different fuel brand These deposits do not affect plug performance |