I recently purchased a new to me 850 and have been trouble getting a grip on the stock 216 belt. At first I sort of liked the way the clutching was set-up. When I would mash the throttle it would overrev a bit to 8350 then settle in and give me a pretty decent 8,100 RPM shift curve. The backshift was satisfactory but would occasionally go haywire in long heated high speed uphill pulls dropping to 7,500 R's (where more slip would happen because of lack of squeeze). I decided to run a couple degrees shallower on the helix (more squeeze) and this helped a bit but did not fix the problem. My primary sheave would get brown and tacky part way through the day requiring a cleaning (I like to ride not perform maintenance half way through a ride). I finally realized that the initial overrev is not the clutching but the inability of the primary to grab the belt, and the weak backshift wasn't necessarily a function of the secondary being overly steep, but was slippage in the secondary resulting in a weak backshift. I cleaned my sheaves this morning and decided to try a Gates Carbon 45C4553 which worked stellar on my 800. The results were spectacular, no initial overrev, just grab ang go, backshift was nearly spot-on with the tack never dropping below 7,800 even at 11,200' in 50 degree conditions. I pulled slope after slope in an effort to create the same heated tacky sheave problems I was seeing with the 216, it never happened. Before I left the mountain I took a look at my primary and secondary, they were both squeaky clean as if I hadn't even went for a ride. Has anyone else found slip to be a problem with the 216 ?