[Healeys] Spark plug color - what do you think

[Larry Varley]

Hi John, keep in mind that a plug color test is best done after high 
speed cruising, ideally drop the car out of gear and turn off 
immediately while cruising at highway speeds for a while. Then check the 
color of the plugs. You can't hear high speed detonation, and high speed 
detonation is what will cause major damage.
Cheers
Larry Varley