These old girls tend to do that if left sitting on the side stand and the fuel petcock left turned on.
When you shut the bike down after a ride, wait 30 seconds before putting her on the side stand in order to allow the oil to drain back into the crankcase as much as possible and turn off the fuel valve. On next start up see if she still smokes.
Not too much of a job. Basically it's a matter of removing the rocker cover, rockers, valve stem keepers and springs and prying off the old seal. The valves can be held in place by pumping compressed air through an adapter into the spark plug hole or you can feed some 1/4" nylon rope into the cylinder when the piston is at the bottom of it's intake stroke then turn the crankshaft to bring the piston back up on the compression stroke until it presses the rope against the valve heads.