dirt bike carbs are a lil different than street bike carbs,on a street bike there is four carbs they have to be tuned toghter,when I had a carbed bike It suck it inloves a lot of tuning and syncing not just two jets and a throtlle slide like a dirt bike

 

If you're around Va Beach lemme know.................I can give you a hand.

 

I would say that most likely it is fouled plugs. Spark plugs for motorcycles are sensitive. Same thing happened to my friends F4 and also my old F3. One minute it started and the next time it just cranked over.