John Deere RX 75 with a Kaw 9hp, this was given to me. It starts right up and runs great till it warms up (about 3-5 mins) then it starts smoking and spitting oil. I changed the head gasket but it didn't help. I did not see any cracks on the head and the cylinder walls looked OK. It does not make any bad noises while running. Is there something I'm missing? Ideas anyone?

I would do a compression test, you could have bad rings.

Pull the blower housing off the engine and see if the head fins are clean.check air filter.
Check vent tube from carb to engine,check reed valve in head.
Luck

I did a compression test right off the bat, it's holding at 180. Head fins are clean,air filter is new,vent tube is OK, and reed valve looks OK. I'm really scraching my head on this one. Thanks for the help

Check oil drain from head to engine , check valve guides.

OK, here is where I'm at. Put all together and it still smoked, bad. Tore it apart again,took the head in for instection and it is OK. Pulled the engine off the frame and tore it down, honed the cylinder walls and re-ringed the slug, all to specs. Put it all together and guess what? You got it, the S.O.B. smokes. I pulled the head today and, with air blew out the breather passage behind the reed valve. With out knowning/thinking, it shot oil all over,, me. I'm thinking that passage was or is now open. Tomorrow I'll throw it together and see. I'm kind of thinking if it still blows smoke, it will make a nice boat achor, I'm not sure what else to try.

Let us know how this goes for you.