I use Coleman or Crown camping fuel, aka white gas. A bottle of this is a good a year later as the day you bring it home.
It's main ingredient is naphtha and I mix it 15:1 or 20:1 with Marvel Mystery Oil or any good 2 cycle oil or both. You can run them without oil but it is not recommended.
There are also 92 or 94 octane pure fuels (no ethanol) that is blended for yard tools which work fine.
Another source, if you have a nearby small airport is 100 octane Low Lead aviation gas. It will have a little less power but is very high quality fuel, lasts a long time, and has no ethanol.
Again, while these engines will run without oil in the fuel, I do not recommend it.
Automotive unleaded fuel now almost always contains ethanol.... also no good for your engine. It absorbs water and eats parts and oh yes, has a poor shelf life.
There are also a handful of poisons in auto fuel which are designed and blended to be pushed through a catalytic converter at 1400-1800 degrees. Our model hit and miss engines rarely get over 110 degrees.
I have bought. modified and resold a few of the M90 and M91 engines. I have added to the instructions Jin provides. (Jin is still learning)
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