An FA50 uses an automatic fuel valve ( petcock ) .
Unless something is not right or it has been replaced with a different style , anytime the motor is not running or being turned over , fuel will not pass until it is switched to the prime position .
If the carb is leaking out of the drain at the bottom of the bowl : the float may be stuck ; the float valve may be dirty ; the drain screw might need attention or the brass over flow tube could be cracked .
In stock configuration , the FA50 runs best with a OEM type foam air filter set up and the carb adjusted per the manual , exactly .
My FA50 started first kick , most often , and held 30+MPH for as long as I cared to ride , when it was totally stock .
Now , technically , it isn't completely stock : less 1 ring and the piston crown has been 'channeled' which lowered the compression a bit slightly quickened transfer and exhaust flow . The carb has been adjusted to accommodate the changes and the bike does as much as 34 - 35 MPH . The piston and rings are due for replacement as both have about 8,000 miles of pretty hard riding .