Stripped it tonight and sure enough the new air filter is black at the front and damp with oil, evidence of oil in the front throttle body and butterfly. Not sure it looks like a couple of litres have gone through there. Would it have gone through mostly as mist and then burnt?
Opened up the casing and the seal is shot. Replacing in the morning and will change out the front plug while we have it open
Did not smoke when we ran it without the airbox and breather hose on so I am keeping my fingers crossed we have the fix in hand.
Thanks for all your help guys
Originally Posted by bloc
Since most of the oil coming out of the breather hose would go into the front throttle body, maybe check to see if the plugs look different front to rear? Surely that kind of oil consumption would leave evidence on the plugs..
I'm not familiar enough with the 990, but on my 950 oil can go almost directly from the breather hose into the front carb inlet via gravity and crank case blowby air flow.. anything getting onto the filter is spray or what has run down the top and side of the box.
All blowby gases must go through small holes drilled radially in the left counterweight, which should have significant centrifugal effect. If that balance shaft seal is bad, however, you lose this system built into the breather to "sling" the oil out of the airflow.