All the major brands specifically recommend using a minimum of 89 or higher octane in their equipment these days.
This is lifted right from the manual for the Stihl BR600M-
"Use mid-grade unleaded gasoline with a minimum octane rating of 89 (R+M2) and no more than 10 percent alcohol content.
Fuel with a lower octane rating may increase engine operating temperatures. This in turn, increases the risk of piston seizure and damage to the engine."
Last edited by Ridin' Green; 04-13-2013 at 06:40 PM.