5D,
Sorry to cause a furor. I wasn't aware there was an amsoil product that was mixed richer than 80:1. All the snowmobile guys where I live run their particular flavour of amsoil at 100:1 (and very happy). The aluminum clutch plates leave quite a bit of deposit behind although I was amazed at how well they handled tha abuse I gave them. When I rebuilt my 92 all the trans bearings were ruined from the aluminum deposits, especially the tiny waterpump ones. The DP kit I got had steel and carbon fiber plates. As for KX500 top end life, alot depends on factors such as how well/often you clean your air filter and using good 2-stroke oil. I recently rebuilt my 92 for the first time after 12 years (about 400 hours est. (+/- a bunch)) of running Belray MC-1 at 60:1. Top end was pristine, I almost could have reused the piston (except for that small crack I found!). I never did a compression test though. In my race career, the first season I used Belray MC-1, I got 104 motos out of my Maico 400 on the same top end, at 85:1. I thought that was pretty good, far from the 2-3 rebuilds I'd normally have done. Been a Belray fan(atic) ever since. Anyway I think the most important thing about oil is to pick a good one (there's lots) and stick with it. There will aways be the leaner/richerand mineral/synthetic arguments (to keep life interesting) but I know that I will always agree with Timbowe & Hoopty on using synthetic oils at a lean ratio. Cam.