ORIGINAL: Bax
If you use a synthetic-castor blend in your 2-strokes, then it won't hurt your four-strokes.
Well my TT .91FS is choking up gobs of black tar/soot into the tank from the muffler on Powermaster. So something in the fuel is burning up besides the Methanol and creating soot. Supposedly that can't happen to castor (not hot enough)...so it has to be the synth.
[But thats a guess.....seems no-one knows for sure.]