i have that problem too, but i cant igure out why. the oil caps may not be tight enough, or there may be a leak or crack in the block. try to not overill it see what happens, or measure how much oil is needed. good luck!
Drain excess oil for engine to proper oil level and run engine to see if it is still leaking oil.
I am assuming this is 5hp horizontal. When you over filled it, oil was probably pushed through the crankshaft seals. Worst case you may have to replace crankshaft seals if still leaking.
Check your air filter element, if unit was overfilled there is a good chance the air filter is full of oil, will choke down engine and cause a lot of coughing and sputtering.
Be sure to drain the engine down to the proper level, when the oil splasher is completely submerged in the crankcase it does not distribute the oil, so even though you have more then enough oil you can still have damage to the top bearings from lack of lubrication...