fleetwin, the purpose of the puddle drain valves it this: As the fuel/air charge moves through the crankcase, some of the heavier fuel particles drop out of the airflow, (think like rain). That results in raw fuel laying in the bottom of the crankcase chambers–both the upper and lower chamber. Too much fuel sloshing around in there makes for lousy running, especially at idle and moreso when you speed up after a prolonged idle. That accounts for much of the chugging we’ve all experienced until it clears out.

So, that is the problem. The two little leaf valves are the solution. Passages from both crankcase chambers are routed to the leaf valves and after passing through them it is dumped into the lake on the older motors. Starting in the late 1960’s effort started being made to route the drainage to the cylinders for burning.

The design of the older motors was state of the art for the day, but in reality was pretty inefficient. They started working on that issue in the 1960’s also. Some Merc guys will be quick to point out that old Mercs didn’t have drain valves. Yep, gotta admit their crankcases were a LOT more efficient.