I don't want to be a naysayer, but I just pulled the muffler on one of my my Stihl 193t's to potentially sell it... This saw has only seen about 2 tanks of fuel since I bought it new (I bought 2 193T's at the same time) and is un-modded in any way. I only used husky premix.
Pretty pissed, my using premix was to eliminate any error in my own mixing, prolong the saw's life, and so I could leave it in the car trunk without worrying about my plastic can exploding.
It has some decently bad looking scoring on the piston, and I don't feel comfortable selling it this way. which sucks, as I do need the money ATM.
Saw runs well, with 175psi compression and passed vac and pressure tests with flying colors, but is badly scored none the less.
I normally use corn free 96 octane race fuel I buy in drums in all my saws, and I have a few saws that have run 180+ gallons of that stuff over the years, with brand new looking internals.