what cause a motor to accumulate oil in the crank case (sumping) ?

 

Off the top of my head, check valve if engine does it after sitting awhile. Scavenging by the oil pump if running. Some others might have better answers.

 

Yep, since your oil bag is higher than your pump, they have a check valve between them.&nbsp\\; If you haven't started the bike, the oil seeps past that check valve.&nbsp\\; Don't be suprised that when you do start it, since the pump won't be able to handle the excess oil, that a bunch doesn't puke out all over your leg.
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Respects,
Ed