[Bobcat]

Interesting what Barry said about plug gaps . I was talking to Rob Pond the other day and he said he preferred .035 gap and no larger than .040 ( for many reasons ) .... every engine builder has his preferences and valid reasons to back them up . Plugs were AR 3923 .
Ernie ... correct , the new MSD ignition systems make it more difficult to read a plug , but where you really must read a plug for WOT mixture is at the base of the insulator , and that is shielded so you can get a good reading of the fuel ring , which will be a ring about 1/16" wide and a light gray if WOT mixture is correct . It takes at least one 1/4 mile run at full throttle and a clean engine cut to be color the insulator .... and a GOOD plug reading light . You can be dead on for WOT and still have a white insulator . Mid range , as you said is more difficult .