i was linked to this thread a while back http://motorbicycling.com/f4/first-c...tall-3532.html
and this link was here
Instruction Manual - Gas Powered Bicycle Engines, Motorized Fast Bicycles, Motor Gas Engine Bicycle, Bike Conversion Engine Kits, Motor Assisted Bike Engines 80cc and 49cc, Peddle Start Motorized Bicycle Engine and more!
if you scroll down this guy says do not use ANYTHING other then a synthetic 2 stroke oil. just thought that was odd.
basically the way i see it natural or synthetic oils make no real difference.
as far as where opti-2 is sold i emailed them before to find out where i could get some, real helpful people, this is the email address i used. firstname.lastname@example.org
i haven't used any yet but eventually i'll change over to it.