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Alright so i bought a new to me sled (2007 XRS 800R with a 151 track) for 1500 dollars it was so cheap because it had a few problems, but the guy told me he had just completed a full rebuild including crank, spi pistons, and rings. Problem 1 was that the D.E.S.S key was not seating properly. Problem 2 was that the clutching was not perfect. Problem 3 was the track was severely worn. Before buying i tried to ride the sled but could only get it to run for a short amount of time and not very strong because of the D.E.S.S key so i bought the sled and brought it home. Later that day i had the key fixed up so that it would run and took it up and down the road a few times, but the sled still did not have the power that it should. So i went to get my compression checker and checked compression it read 62 lbs identically in both cylinders.. I didnt think that sleds would even run with compression that low?? So my first thought was my compression checker was reading low so i checked my 04 rev 800 H.O. and it pulled 140 which is correct. So i called the guy and told him that it was a done deal anyways and i just needed to know if he really done the rebuild which he still claimed he did and used spi dual ring pistons. I ran the sled for about 6 hours on saturday to see if the rings would seat and compression moved almost to 70 lbs in each cylinder which is not a big difference. So long story short my question is do i tear down and assume that he did not complete the rebuild or perhaps got junk pistons? Or can anything else cause the compression to be that low and still allow the snowmobile to run and idle great but just have a loss of power? I also just cleaned the valves last night and it did not run any better. Thanks in advance.