Ok so this may be completely wrong and outh there but can the wrong size fuel line be letting in too much gas and causing the carb to flood, which no matter how clean and well adjusted mine is it will still spit out gas? When I bought the quad in the summer it had a piece of Goodyear line which is still on it.
No, line size will not cause carb overflow.
Take the carb off, put a clean line on it and try blowing through it.
Take the float bowl off the bottom of the carb and see the effect the float has on blocking or allowing fuel.
By blowing thru the line you should feel any leaks or see if the float angle is right.
Worn seat or needle, divot on the tab, loose needle valve seat, all good got-cha's.
Steve