If the carbs are overflowing you have a float/float valve issue.
Did you remove the floats and the float valve? The float valve has a spring pin on the end where the float "tang" hits it.
Does that work smoothly? Does the float valve move freely in the seat/holder?
If you have brass floats, do they look crushed /expanded or properly formed??
If you shake a brass float, does it have gas inside it? (eliminate sunk float possibility)
If the float system is not working properly, the carb overflow upsets the mixture delivered to the engine.
If you had gas collecting in the filter box, how do you know it didn't also travel though the intake runner, past the valves, the piston rings and pollute the oil supply?
The engine may not need choke to start if the O.A.T. is high.
Are you parking on center stand or side stand?