If there's enough blowby to get much vapor out of the top vents, the piston rings are worn out. Below 30 MPH there's not enough airflow past the end of the road draft tube to create a vacuum in the crankcase. A slight amount of vapor coming out of the valve cover slots is normal at idle and low road speeds, but if there's a noticeable amount of blush smoke puffing out of the top or bottom, it's engine rebuild time.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!