Your 49cc engine starts up but when you take off the choke off its dies?

There is a idle screw above the gas lines. Turn that out 2 1/2 360 degrees

It would be better to turn it counter clockwise 1/2 turn at a time and see if it starts and runs. By turning it out 2 1/2 turns right off the bat, you could flood it.

If none of that works you may have to clean the carb, flush the fuel tank and lines and replace the fuel filter.