Had an interesting chat w/ the guy from Amsoil this morning at the Woodsman show up in Bangor... Says they really do say to run it at 100:1, but even he goes a bit rich from that.
However what I he said that I hadn't heard from others, which made a certain amount of sense, is that if going from dino to synth, regardless of brand, in an engine that's been used for a fair while on dino, you should do a slow transition, rather than a "cold turkey" switch. I.e get a gallon of each blend, and alternate them, or do a couple tanks of half synth / half dino...
His reason is that he said the synth is a good high detergent cleaner by it's nature, and that it WILL remove any carbon buildup in the combustion chamber... However if you do a rapid switchover, it will do the decarboning in a very short interval, with the potential of knocking loose big chunks that could get into the rings and such before the normal combustion process could clean them out. By doing a more gradual switchover, you also get a slower and safer decarboning... Don't know that it would make a huge difference in a newer engine, but can't see that it would hurt.
Gooserider