This is logical, correct?
 

A monthly procedure is to drain the accumulated oil out of the air box. There is never any oil from the left side drain, only from the right side one.

This would be because the crank vent tube dumps to the right Throttle Body. Correct?

Then, why the left side drain?

JonyRR - I know what you're going to say and a winter project just might be to run the tube out back and add a nice, small K&N filter. I note that Nate Kern's bike(s) just dump the oil into the air box with the stock set-up.

In stock configuration, why doesn't the air filter get oiled up?

The bike leans to the left on the sidestand, thus the drain there.

The drain is not just for oil but other liquids the system may injest as well.

The air filter doesn't get dirty cause the dump is below it or down stream if you will.

BTW, Jim, if you are reading this thread, ever think of a vacuum pump connected to the crank breather? It was worth 5 mph on my drag bike. Might do wonders for a top end run over there in NC.

If you keep the oil level no higher than the "red dot" in the center of the oil inspection window, you will keep the airbox ( mostly ) dry of of oil ( and knock down the pinging on hot days, too! ).

jeff

A reed valve assembly has been used before on the late seventies racing Beemers to reduce the crankcase pressures. I've always thought it would work well on these bikes.

A large flexible line was ran to a foam filled box under the seat and a row of reed valves was fitted to the top.

Must give it a go, one of these days.

Cheers
Trevor