[steve86]

Older motors, like my 70’s dirt bikes, were designed for the lubricants of the time. Hence, the 20:1 recommendation. Even the cheapest Walmart premix now is far superior to what was available then.

But, by all means, if you know in advance that a heavy load scenario is likely, especially with high operating temperatures —say like a dirt bike tractoring through deep sand on a hot day — go by the manufacturer’s recommendations or reasonably close to it (i.e. don’t use 80:1 if the owner’s manual calls for 40:1).

I don’t have a gas chain saw but being air-cooled and used in high-stress conditions I imagine the use can fit into the “severe” category quite easily.

[tomkat]

Well, if my math is correct, the difference between a 40:1 & a 50:1 mix for one gallon = .64 oz.

So, apportioned into 128 ozs of fuel, the difference per oz. of gas is .005 oz of oil ?

Yep, worth a try . . worst case, the J will die and can be tossed with a clear(ish) conscience !

lol