Ran 927 for 9 years in by banshee 2 different motors. Just tore the topend off my most recent build 5 years and very little carbon on the piston. I run 40:1. I guess if you run 32 and your jetting is a little off or you lug it a lot it could build up. Who knows. Also im in NE Ohio and Ive rode it in 7 Degree days with NO problems. Never blown it up never even had low enough compression to need a rebuild. Just rebuild to change things up. 4 years on stock top end and 5 on a FAST 4 mill. That being said Klotz what I would run if I didnt run 927.