Did you rip the new gaskets? That would be a cause of the poor running - i mentioned in another thread about my 99 murray hydro with a 17HP briggs twin - i took the carb apart many times, super cleaned it and put it back together, ran terrible or not at all - the original gaskets were all swelled up, almost dryed out looking.
I bot a carb rebuild kit, put all new gaskets and pump rebuild kit in, thing practically fired on the first hit of the key and ran awsome - new gaskets do make a difference.
Does the motor also have a antifire solenoid on the bottom of the carb float bowl? Those can be a serious annoyance as well - when they get older, they stick out and cause fuel flow issues - it can be tested out of the machine- turn the key on ( w/o cranking the motor) - the solenoid should retract- then when key is off- it should extend. If its extended with the key on- that can cause the running issues.