If it's filling up with gas it's your needle and seats in the carbs leaking. They would be replaced with a proper carb rebuild including all new Mikuni parts.
If is filling with oil then it is your inner crank seals and the only fix is to install a remanufactured crankshaft.
If is filling with oil then it is your inner crank seals and the only fix is to install a remanufactured crankshaft.