I've been using AVGAS (100LL) with Klotz @15:1 in my FG-60 since I got it thinking it'd be the best fuel to head off potential detonation and the fact it has no alcohol in it. I have been having some problems with carbon/sticking valves mostly on #3 cylinder which for some reason runs the hottest. I've changed over to a Morris ring/ 30 deg timing and it seems to run a little smoother/cooler. Haven't had a chance to fly it yet this year. Field is to soft/wet to fly heavy planes.