Iam running a L86C champion , gapped at 28 and its running smooth my top speed on flat ground has been 37.9 mph and Iam happy with that!
Just give it some time!!
Seriously - I've used Champion plugs from time to time since I was 15. EVERY ONE I mean EVERY ONE has fouled on me. I'm now 50. Three stories.
1) Suzuki TM125 - Champion plug. Fouled within an hour. NGK perfect.
2) Datsun 510 - Champion plugs. Gap perfect, nothing else changed. Within 1000 miles, car difficult to start. Soon, wouldn't start at all. Install NGK, starts right up runs rest of it's useful life on NGK with no issues.
3) Screw this, let's go fishing. Friend's four banger boat. Fresh plugs and off we go....we are trolling....engine starts missing really bad.....nice....out in the middle of the Puget Sound....well we can fish some more....we lose another cylinder....oh man we better head back, thank God within 100 yards of the boat ramp we lose cylinder #3.....so we make it back and I ask him what kind of plugs he used.... "Champion".....
4) Chainsaw maintenance time. Runs sweet, but I figure I'll get a new plug. All they have at True Value is Champion. Install the new plug. Won't start. Put old plug back in. Starts right up.
I think I learned my lesson.