Had a similar issue with the stock TT250 carb. A little hesitation at 3/4+ to WOT. Swapped to the mikuni, issue gone. I did see the following in another thread.
http://www.chinariders.net/showthread.php?t=17824
http://www.chinariders.net/showpost....0&postcount=49
Adjust the float level to allow more fuel into bowl seems to be the ticket.
Rojo