I have been using Amsoil 100 to 1 synthetic 2 stroke mix for 4 or so years now. I have been mixing it with any name brand 87 octane fuel such as Exxon, Sunoco and Citgo. I have never, ever had a problem until yesterday. I was happily earning money when all of a sudden my Stihl BR420C looses a little RPM and then goes right back up. About 10 minutes later it does it again only this time it lost RPM for about 5 seconds. With-in about 20 minutes the blower won't hardly even run. After 30 minutes it just quits. I disgustedly take the blower back to my shop and check for water. Nothing. I checked the fuel tank breather and it's in good shape. Replaced the fuel filter and still the blower runs like it running out of gas. I pulled the carb off, took it apart, sprayed it down with some carb cleaner and put it back together. It still won't run right. So I went to the local Citgo, bought some fresh gasoline, mixed my Amsoil in it, dumped the old fuel out of the blower and filled it with the new mix. No change. I called my buddy and arranged to try some of his fuel. He uses 89 octane Citgo with Shindaiwa 2 stroke oil. We put the fuel in and it runs like a champ. No spits, sputters or hesitation. Now bear in mind that our state mandates a switch from oxygenated fuel to super oxygenated fuel in the winter months. Do you think the problem is with the fuel or the Amsoil? Or could it be a problem of the Amsoil not wanting to mix properly with the fuel or contaminating it somehow? Any ideas?