Became a LOT more difficult for the back yard tuner when they took the lead out of gas. ive done a lot jetting motorcycles, car engines not so much. This is a real useful article if youve done serious changes w/ the cam, carb, and compression. these tests are done by killing the ignition at the RPM you are interested in, going up a hill, and hauling in on the clutch the moment you kill the ignition so the engine dost overrun, which will change what the plugs look like.
https://www.dragstuff.com/techarticles/ ... plugs.html