all i work on are 4 stroke stuff if its black its gas .and its not valve seats its
the valve guids or guid seals that make a engine smoke on start up but thats blue .your carb is leaking fuel when the engine is turned off .and it clears up once burned .if it was a head gasket it would not clear up and would lack power .if you can raise the carb up and put something under it and you will see were the fuel is coming from .Bottom line gas is in the motor when you fire it .unless the choke is sticking.Good Luck
Got to disagree with you on this one. When the gasket starts to go between the push rod galley and the cylinder, it will smoke on start up but will quickly go away. The head and cylinder heats up and expands, squeezing the gasket tighter and the leak stops.At least at first. There will be no noticeable power loss. As the leak gets worse, and this can take some time, the smoking will continue even after warm up.
I only mentioned this because I had the same problem as the OP, and this ended up being the problem. Replaced several head gaskets on the Kohler and only after the head was replaced did the problem cease. The head was checked each time for being flat, it was .03 out of flat, the kohler specs called for .04 or greater before the head needed replacing. The last time Kohler sent me two new heads and the problem ceased.
I would only pursue this avenue after fuel was eliminated as the source.
One way to eliminate the gasket problem right off the bat is to pull the plug wire on one cylinder and see if the problem persists. The next cold start pull the other plug wire. If it still smokes during start up, chances are the heads/gasket are okay, small chance that both went bad at the same time.