Motorcycle Repair: 1990 Evo check valve replacment., crankcase breather, pressure relief valve

Question
I believe my oil pump check valve is malfunctioning.  After long periods of
sitting, oil pours out of the crankcase breather tube, out the air filter and forms
a puddle on the floor. My service manual is lame. No info on diagnosis, repair or
replacment. I need to know more about this common problem. Also I would like
a referal for a shop manual that addresses this in detail.  Any help?

Answer
Your check valve is under the big slotted screw head on top of the oil pump.  There are two.  The one closest to the crankcase is the check valve.  The one on the outside is the pressure relief valve, it has a metal cylinder inside it.  The check valve is just a ball bearing held down on it's seat by a light spring.  You should replace the ball and spring.  I have a homemade tool made from a used check ball tack welded to a wheel spoke.  I put a dab of lapping compound on the ball and lap the seat by spinning the spoke.  Oil from the tank pushing out constantly keeps any compound from going into the cam housing. Then clean it out with brake clean.  You can always route your breather hose down between the crankcase and tranny instead of into the air filter.  Lots of aftermarket "breather filters" available to put on the end of the hose.  Always run your motor until warm before changing oil so any crankcase and cam cover oil is back in the tank.  Otherwise you will be having an overfilled system and always getting oil out the breather.  Don't know of any service manuals other than HD #99482-90.