I HAD A FRIEND THAT BUILD HIS OWN MOTOR IT SMOKED LIKE CRAZY
I KEPT TELLING HIM FOR MONTHS HE HAD THE BREATHER VALVE NOT TIMED CORRECTLY WAS MY GUESS
HE BROUGHT IT TO ME AFTER SCREWING WITH EVERYTHING ELSE
IT TURNS OUT THE MARKS WERE ALL LINED UP BUT AT SOME POINT SOMEONE HAD MODIFIED THE BREATHER HOLE IN THE CASE IN THE WRONG DIRECTION
I MOVED IT ONE TOOTH REMARKED THE BREATHER AND IT FIXED THE PROBLEM
Did it foul plugs, or just smoke?
It might be time to ask this guy if his trouble started around the time his cam cover was chromed.