tweak the float height if its leaking fuel. yes, sometimes you gotta do it five times, until you finally dislodge that bit of hair stuck in the needle valve. frustrating but true.
or just be thorough the first time
my main suspicion is the valves for the easy start, then cough cough kusplut, and then starts again once its had a chance to cool slightly. valves stretch when they get hot. clearances get tighter. inadequate clearance when cold, followed by a longer valve= no closie the valve!
easy check on that is to just back the adjusters off by half a turn. let them click and tap! if it cures the issue, then you can adjust them correctly. theres always the chance of a badly seating valve, eccentric seats and all that, but pretty unusual.
thats always been my trick...make sure its too rich, make sure valve clearances are too large, and if things get better... start adjusting/tuning, one thing at a time, until perfect...
i cant comment much on aftermarket carbs, other than...mikuni has a reputation for being good, simply because they ARE! never touched oko or molkt, always been a stock, a mikuni, or a keihin for me... a wise man spends money...um...wisely. sometimes. dam you ebay!