Originally Posted by Twin-shocker
In choosing a 2T oil for pre-mix bikes, make sure it states clearly on the packaging "PRE-MIX ONLY", as any 2T oil which can also be used in injector oiling systems, is not fully synthetic, and ideally should be avoided for use on pre-mix competition bikes (its thinned 20% with kerosene, so it will work in injector systems).
That, I understand clearly - NO injector oil, nor "works in BOTH injection and premix" BS. I like the Bel-Ray MC-1, http://www.belray.com/bel-ray-mc-1-r...-2t-engine-oil
, says it's for old air-cooled 2T's, may give it a go next time. (but it is awfully pricey, $$$) When I got my old YZ, the externals - engine, pipe, etc. - were drenched in oil and dirt and baked-on oil/dirt. Possibly the P.O. was running a 20:1 castor mix; maybe it has preserved the motor internals.