First off this is not another "which oil is better thread" - HONEST! I have a lightly used 2000 WR400 which I'm guessing has less then 200 miles on her. I've put 3/4 of those miles on the bike so I know that the oil and filter has been maintained properly for most of its life. So here's what happened and I can't understand what could have caused this... It was my 3rd oil/filter change on the bike and I decided to put in Amsoil's full synthetic motor oil. With the crappy weather we've been having in the northeast I didn't ride it after the change for probably 3 weeks or so, but this past Sunday was nice so I took her out. While the bike was a bit harder to start due to the colder weather, I was able to light it up after 6-10 kicks and then let it warm for a minute while I got ready. Well I pull out and the bike stalls (again no big deal) HOWEVER when I went to kick it over I noticed that I didn't have to pull the compression release. In fact I could easily push the kick start through by hand... While visions of dollar signs were flying through my head I started pulling the valve cover apart expecting the worst. Well to make a long story short everything looked fine. Timing chain, compression release lever, valves - everything was perfect. I noticed as I was testing things and pushing it through with the kick starter the compression was slowly returning. Do you folks have any idea what could have caused such a drastic <<but temporary>> loss of compression? Really the only change that I made was using Amsoil. I rode the rest of the day and the bike ran well, there was not any smoke and everything seems perfect. It's just weird - any thoughts on what might have caused this?