Know about the adjust the flow stuff. My reason for asking the question is wether or not anyone has disabled the stock system. I for one didn't like the fact that the crud from the clutch and chain were sucked back into the entire oiling system. When I took the rocker covers off the engine back in '85 there was a coating on every surface in the motor. There is no reason for this in a modern engine. That is contamination which I don't need. I just use 3 oz. of ATF tytpe F for lube. I have the dry clutch. It works just fine and the engine stays nice and clean. There is a side benifit.
In the pre '92 EVO engine cases the return oil from the primary is sucked back into the engine. If this fitting is used in conjunction with a baffled catch can, the breather tube can be routed to the can and any oil expelled by the breather can be sent back to the engine. This makes the breather system a "closed" system as far as the oil is concerened. By mounting a small filter like a K&N crankcase filter on the top of the can you can make an loseless oil breather systm, eliminate the original breather hose to the carb, plate and clean up the whole look of the engine.
There is one caveat here. If the engine wet sumps after winter storage or the oil pump check valve is not good, the oil pumped out of the breather will overwhelm the catch can and make the small breather filter on its top your first indication that you have a sumping problem.