Riding mower floods out?

1987 Honda riding mower floods out spiratically once running for a long time. I cut two 1/3 acre lawns once a week, and about 3 quarters towards finishing the mower will start smoking and loose power. if I remove any loads on the engine, it stops smoking and is good for another couple minutes. I am assuming that it is flooding out, because now i see fuel pour out of the carb intake when it begins to smoke. I cleaned the carb, and even tried a carb from my parts machine, which worked fine in that mower, yet it still does it. Fuel filter is fine and i don't see how the fuel pump could be the cause, as a friend suggested. My only thought is there is a 2nd hose coming off the carb that runs to this little box, which i suspect is a breather and possibly it is clogged? but i blew it out too and still the same issue