I have a 2000 WR400 that is running the auto decompression exhaust cam from a 450. I did the mod two years ago and have never had problems with how the bike runs but, a two weeks ago I put in new piston rings (Wiseco piston, stock size & compression) because the oil ring hadn't seated very well previously and I was burning quite a bit of oil when riding. Swapping the rings was easy and really only took a few hours for the full teardown and re-assembly of the cylinder and head but now, I'm getting blue smoke from the exhaust when I fire it up (it gets better but doesn't go away 100% after warm up and riding). I also noticed today that there is air PULSING from the valve cover vent hose - the pulsing is consistent with the bike's RPM. If there is loose dirt on the ground below the bike, the vent hose will actually blow it around. I thought perhaps I had the timing a tooth off and was getting some blow by but, I just opened up the valve cover and found that my timing is accurate based on this: http://www.thumpertalk.com/forum/showthread.php?p=3706078#post3706078 Does anyone have any suggestions of why there is so much air being pushed out of the vent hose? I'm relatively sure it will be the same issue causing enough oil to get burnt and cause the blue smoke.