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The China motors are pretty crude by todays standards. That's why you need a 16:1 mix for braek in. They haven't used that ratio in much of anything in the US since the '70's most premixes are 40:1 =poulan or 50:1 which is most all outboards, chainsaws ect. This motor wants 25:1 normal.
The easy way is to go to a marine store. they sell premix bottles. They are marked all over. Just turn the bottle to the mix ratio you want. Fill up to he line for that mix and the # of gallons you plan to mix. Then pour it in the gas can and add fuel. All auto parts stores and wm ect sell 2 stroke oil.
I've thought about doing this to a bike for a couple of years. 2 probs. I don't want to add it to any of my existing high end bikes. About 1/2 mile of my commute is just a crazy dangerous mismash of merging. I've bike commuted for years but this stretch of idiots keeps me from commuting to my work location on a regular bike. These 50cc engines aren't really much faster than pedalling. So no advantage in traffic.