I have two of these old engines in a 36ft boat. One engine is great and never gives any problems. The other one has a tremendous amount of blow by. The engine runs great, starts immediately even in cold weather, and has plenty of power. It has very little blow by coming from the oil pan when the dipstick is removed but is blowing like a leaf blower out of the valve covers at high rpm. At around 1200-1500 rpm a pulse of air can be felt coming out of the oil filler hole on the valve cover like it is a cylinder's compression leaking into the valve cover. Does anyone have any idea where this could be coming from? I know that usually blow by is caused from compression leaking by the rings but this seems to be going the other way. Any help would be greatly appreciated!