Normaly if your piston s white clean-it means it didn't work yet. Even after 2-3 tanks of work on racing tuning, it should became dark brown and later black. It doesn't supose to collect varnish and if it is, as Slotmachine mentioned-that fuel isn't the best. Try to use some very well blemded as O'Donnell, Bayron. I have very good expirience with them. Also, you can contact to Stefan and if you live in his area, he is blending very good fuel, I recomend it to you.