YCF 50 A Owner's Manual page 125

The type of specific fuel for your Mini-Motorbike can be found below under the "Fuel Requirements" section.
Your Mini-Motorbike has a fuel tank capacity of 3.8 lt (1 U.S. gallons) incl. a 1 lt (0.26 U.S. gallons) reserve. It
is not recommended to use fuels with an octane lower than 87 that would produce sustained audible knocks,
as engine damage will occur. YCF supports the use of cleaner-burning fuel. Therefore, the use of unleaded
petrol is highly recommended.
In addition, do not fill the fuel tank with an oil/petrol mixture.
Fuel Requirements
Use clean, fresh unleaded petrol with a minimum Antiknock index of 87. This rating measures the fuel's
resistance to detonation, commonly known as "knocking". Using a lower octane may result in reduced
efficiency and power.
Oxygenated Fuels
The alcohol blends listed below are commonly used instead of standard gasoline. Please check with your
authorized dealer prior to using anything other than standard gasoline.

Ethanol

MTBE

Methanol
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FUEL