I would check the plugs for fouling, then check your crankcase breathing system to ensure it isn't clogged. Also keep an close eye on your front and rear main seals, those are sensitive and overfilling the crankcase can make them leak. Also depending on your type of oil separator you could have gotten oil down your intake, check out the throttle body for oil, if you have any clean it up with some emissions friendly cleaner.
Good luck

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Brian W. Heitman

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