I think there's a compression virus floating around this thread. XYZRacer lost compression a few days ago for no apparent reason and today a very weird thing happened to me. It was the first ride/break in run with the new hotcams and 430 kit. It was around -30 and I cruised around for about an hour with no problem. I figured I'd open it up a bit so I headed out onto the bay and was cruising along in top gear about 60 mph. After about 5 minutes she grogged out like a 2 stroke melting a piston and I rolled to a stop. I hoped that the carb had just iced up and tested the kickstart slowly. There was almost zero compression and then the kick lever stopped solid. I figured for sure I had bent a valve. 2 of my intakes were a tad tight and the new shims hadn't landed yet and I was crackin' to get out riding. I figured she got hot and a valve kissed the piston. I put the bike in gear and rolled it backward a bit and then tried the kick lever slowly again. It turned a bit and then brought up solid. The only thing I could think of that would lock up the engine at a certain point and cause a loss of compression was a bent valve. I sat on the bike for a few minutes thinking about the long cold walk back to town and then I rolled the bike backwards and kicked again and it kicked through, but still no compression. I kicked slow a few more times and it turned freely which was strange since I didn't put enough pressure on the lever to push the valve away from the piston. Then I think that I cracked another throttle plate and a bit of metal was stuck under a valve holding it open and fell out when I turned the engine backwards, but the valve wasn't sealing. I waited for a while hoping a sled would come along and now and then would give it a few kicks. Gradually the compression started coming back. I'd get a little pop but with the low compression I couldn't kick fast enough to get it to run. After an hour a few friends happened by on sleds and I got one to tow me to try a bumpstart. He dragged me for half a mile before it finally caught and was running crappy but I kept it running and aimed for home. In a few minutes the engine cleared right up and was back to normal. I took it to the shop, checked a few things, found nothing, and went back out and rode for 3 hours solid running perfectly, all the while trying to figure out what the heck happened. Then I wonder if it is possible that an intake valve iced up and froze open. I've run the bike longer and harder in colder weather and never had this problem. Then I think that maybe the higher lift of the new cams is pushing the valves deeper into the guides and crap buildup is causing them to stick, but why only at high speed and not high revs in lower gears? The bike is running great so I head back out onto the bay for a test and sure enough after a few minutes she starts to crap out again. I pull in the clutch and keep it running and after a minute sitting still it clears right up and works perfectly again. It was getting dark and I was half froze so I headed to a superbowl party to thaw out. I'm gonna do some more testing but this one's got me stumped. Anybody have any ideas? Any spaceships in the area lately? Aside from the compression virus I had a great ride. My bike has been apart for months and it felt good to hit the slopes (although it's gonna take a while to toughen up to that brick of a seat again). One nice thing about riding in the snow is you never have to wash the bike. Here's what it looks like after 4 hours solid riding. My helmet vents iced up a lot and I had to stop every half hour and chip the ice out with a key so I could breathe, and I got a touch of frostbite on my cheeks, but that's just part of the deal up here.