It may be the following reason:
1. Please check if the fuel valve is open and the kill switch is off.
2. Fuel:91# gasoline; Mixture ration of fuel and oil is 20:1~25:1
Use regular 2 stroke oil (easy to find in super market) and 91+ octane fuel. Ratio mix should be 1 gal of fuel to 5.5oz of 2 stroke oil. You can also use the mixing bottle provided with the unit to achieve proper mixture.
3. When the engine is idling, it is easy to flame out, indicating that the idle speed is too low, and the idle speed adjusting screw can be adjusted clockwise for half a turn. Second, idle speed is too high after starting, bolt rotates half circle counterclockwise. Specific clockwise or counter-clockwise adjusting range, in order to adjust to the stable state of the engine can be the purpose.
4. The damper is opened at start up. If the damper is not closed when starting, it may also be flame out. The up is open and the down is off.
5. In the case that both of the above problems are not feasible, there may be a problem with the carburetor.
Here is the link of how to start your dirt bike：https://www.youtube.com/watch?v=_VR1BzrqYj8
To save back and forth, we need a clear description of when the bike stopped working, what symptoms the bike showed before stopping to work, any noise and missing parts, any leaking, as detailed as possible.
Sorry for the inconvenience.