[Rev]

You will have to do a full throttle run for 1/8-1/4 mile and then shnt off the ignition and coast to a stop in neutral (with new or good plugs). Then pull the plugs for a reading, I make a template out of cardboard with a hole numbered for each cylinder, so as to keep up with the individual cylinders.

Now with the plugs in the template, note the color of the INSULATOR. Not the ground strap or any other part of the plug. Tan is ideal, Gray is still OK. Dark brown is somewhat rich, and black is way to rich. Light white is too lean.

These guidelines only pertain to wide open throttle. Part throttle settings are another determimination.

Rev