Well I have ran about 4 tanks of chainsaw oil/gas at 40-1 and I decided to use the synthetic oil that came with the M290 blower. I dumped all remaining fuel out of blower back into saw mix can. Placed complete new synthetic mix in it and she ran even better!!! The RPM picked up more. It really pushes air for a small blower. It is sure handy to have. Got to find another for a plane...yup its that nice!!!!