Try this first, drain all the gas out of the tank and carbs. There are screws on the bowls on the carbs you open up to drain them, it should come out the overflow hoses. Replace with fresh gas and try it out. If yours has a fuel filter replace it. If your bike has a PRI or Prime position on the fuel valve put it on that. If it still acts up open the gas cap and run it with the gas cap off. If that fixes it it means your cap isn't venting.
If the fresh gas, differnt position on the valve, no gas cap and fresh filter and whatnot doesn't help you'll have to dig deeper.
If the fresh gas, differnt position on the valve, no gas cap and fresh filter and whatnot doesn't help you'll have to dig deeper.