Re: 100:1 Mix
I race karts as well and one thing I have learned is that all oils are not created equal in what I have experienced on the track. I race 4 strokes and not 2 strokes, but there is no way I would run conventional oil in my crankcase. 14oz of Amsoil 5w30w has served me very well. My father n law however does run a vintage West Bend 2 cycle powered kart with a conventional oil mix of 16:1. It works out well for him, but I feel sorry for the poor fellow running behind him eating all that smoke and excess oil shooting out the header.
My point is run what works for you. My father n law could never be convinced to run anything other then 16:1 in that 2 cycle west bend because he gets the results he wants from using it and trust that mix. Same goes for the Opti-2 I run in my bike at 100:1. It performs to my satisfaction, is clean burning and has never given me a reason to doubt it. However...if one is not comfortable with the idea or has had a previous problem like you did with amsoil 100:1....then by all means I would say do not use it. I guess it all comes down to ones experience with a product and thus far I report to others that mine have been positive when asked about opti 100:1. If someone blew a piston on the stuff...then I want to hear that to.