As no mention to running or maintenance lubrication per instruction manual, it would seem, as marketed, this rubber O-ringed engine series is really intended for short run, novelty duty cycles. I'm not aware of any serious working engine design, 2 or 4 stroke, that attempts to adequately
lubricate the piston skirts, rings or cylinder wall via fuel mix thru the intake port on the Combustion Side of the piston/rings assembly as it would have to be so oil ratio rich as to have serious sooting issues. With open crankcase, No lubricant splash features, direct pre-run oiling of cylinder wall, piston skirt & pin for short demo runs is about it unless you accept early parts replacement & frequent head off soot clean-outs of fuel mix only lubrication, imho.....My M90 runs so cold, that straight, non-lubed Coleman fueling is probably going to cause plenty of incomplete combustion soot generation alone without trying to add more partial combustibles in a "Top Down" fuel lube attempt..just my newbie, re-evaluating this cool but very unique, out of the box, probably needs a few lube tweeks, well done execution...tom.