We really do not have enough information to give you a good answer.

If it is brand new it might be because it is still "breaking in" the engine which is where everything is new and kind of needs to seat in. That can take a bit of time depending on the oil that is in it.

If It is kind-of-new, then it might be because of not breaking in the new engine correctly. If the engine is run at a set RPM all the time, then it can wet-stack, and smoke or pump oil out of the exhaust.

If its been an engine you have been running forever, then it could have a broken ring, or worn rings.

Or it could be as simple as, being an air cooled engine, it has not got up to temperature yet, the cylinder and piston have not expanded quite enough to give a good seal against the oil rings. But as soon as it comes up to proper temperature, it seals and stops smoking.

The motor has about 450-500 hours and it only smokes when I first start it.

Black smoke, blue smoke or white smoke (not talking about some possible water vapor at first in cold weather)? If it's 'blue/black', it is the result of a rich condition where the choke is too closed and too much fuel is in the cylinders. This 'washes down' engine oil in the cylinder and burns it. Blue smoke is just oil. White smoke is also oil but usually coming in at the valve seals.

Your engine might just be wearing out early for any number of reasons.

Black smoke is too rich but not washing down oil YET! Fix that choke now and avoid irreversible damage.

ok