- Light tan: Great fuel mixture and air-fuel ratio. That means nothing goes wrong, and your engine is operating well.
- Black or dark brown: The engine probably runs too rich. These spark plugs will feel a bit dingy under your hands.
- Oily and black: Fouled oils. In that case, continue to inspect the piston rings or valves. They are the most likely culprits.
- No colors/light grey/white: The most worrying condition of all – since they clearly imply lean-running engines.
- Worn/eroded center electrodes: Symptoms of a plug long past its peak.
- Flattened or broken electrodes: You probably have set up inappropriate/wrong spark plugs. Spark plugs too long may cause engine damage, while short ones result in spark plug foulings and terrible gas mileage.
- Blisters on insulator noses/white carbon deposits/melted electrodes: Hotter plugs than required.
- Wet plugs: Check whether your engine is flooded.
i read those plugs as lean running , when we rolling road these engines we always aim at choco brown darker the brown the richer they are under load, these engine need slightly rich fueling to stay together when nailed hard, the only thin that cools the combustion process is the fuel at that point , lean the pressure and heat builds up so much and will hole a piston crack a valve even impact crank on point of melt down by pre ignition if caused by timing chain way out, yours look to be grey and have black carbon where not in the heat ball as such ,,