Outdoor Power Equipment and Small Engines - 8HP B&S MTD lawn flight

I have a older riding mower & iv cleaned the carb & replaced the coil and now it has a great spark but when i start it it fire's up 1 time a bit of smoke comes from the muffler and keeps braking the flywheel key. any ideas?:confused:

As for the timing (flywheel) key, the tapers of the crank and flywheel must be free from burrs, the crank threads must be good and, most importantly, the nut must be torqued down to 65 ft. lbs. As for the smoke from the muffler, it depends on what color it is as to what the probable problem will be. White smoke indicates fuel dumping from the carburetor into the crankcase (I'll bet this is your trouble) and would require you to soak and recondition the carb. Blue smoke would indicate either an overfilled oil situation or blow-by past either the piston rings or the valve guide(s). And, black smoke would indicate a rich fuel condition being either a plugged/clogged air filter or a carburetor way out of adjustment.