View Full Version : Reading Spark Plugs cheat sheet

08-24-2004, 09:04 PM
Thought this would be good to show how plugs burn

08-24-2004, 11:44 PM
Not bad, but going by colour alone can be very deceptive. I have seen perfectly jetted engines (as in perfect EGTs and piston wash) that have had plugs that burn either lighter, or darker than what many people perceive as being acceptable.

My rule of thumb is to be more attentive to where the transition in colour occurs on the side electrode. A properly jetted engine will show the transition right on the radius. If it occurs closer to the base then the engine is lean. If it is creeping over the top then the engine is rich.