[Cthulhu_]

Probably motor oil, these mopeds normally run on a fuel/oil mixture.

[bullen]

True, so he injects the motor oil with the gas so the cylinder doesn't jam?

But has he prooved there is only lubrication oil in there, oil also burns, maybe the methane bubble is just for show and he has actually converted the engine to some sort of diesel/ethanol/any other oil engine! ;D

I want to se the engine stop when the ballon is empty! :\

Also now I watched the video: he spends more energy collecting the gas than it would have taken him to use a regular bike. But fun idea.

[cartoonworld]

Moped is a 2-stroke engine, the fuel is also the lubricant, It won't combust on oil alone.