i actually had the same problem with my maxi after kitting the bike - i got ahold of a 70cc kit and performance pipe but didn't have the cash to drop on a bigger carb at the time. this resulted in the same symptoms - running way to rich, bogging at takeoff until enough air got into the mix, fouling plugs every now and then. it was very telltale too, since the bike would run fine when it was cold, but as soon as it warmed up it would start hesitating whenever i would give it throttle at idle. however, i recently came across a 14mm bing for the bike and the result is stunning... not only did this solve the problem of the bike hesitating at takeoff (after downjetting slightly), but the top speed is ungodly now. it wasn't a slowpoke before, but i feel pretty comfortable in guessing that its pushing close to 50 judging by the traffic that i've been pacing.
i did have some luck earlier with the stock 12mm by downjetting, although this is undoubtedly a bit dangerous, especially if the cylinder is still being run-in. i read that you picked the bike up with the kit on it - any idea as to how much time the new top end has on it?