I recently changed from Phillips 93 to Amoco 93, wondering if there would be any improvement in throttle response, etc. There was nothing significantly different in the way the bike ran. Bringing in the air screw about a 1/4 to 3/8 turn was about all that was necessary for jetting changes.
However, one odd thing I noted was that the plug now has a nice tan/caramel color. With the Phillips, the plug was always blackish dark brown. I'm not a jetting guru, but the bike was very close to being spot on. I could put in a new plug, and in an hour and a half of riding it would look like an old plug. I finally quit worrying about how the plug looked, and paid attention to how the throttle response and power felt.
So why would the Amoco fuel leave such a clean insulator? More junk in the Phillips fuel?
KDX200/ FMF K-35
158M, 45P, BEM-3, 45 deg, 650'