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Can be blow-by caused by worn piston rings or valve seals, but I'd check compression and make sure your crankcase breather system is up to snuff. (.e.g. not blocked and hoses are good.) If it's just a little bit and you're not burning oil, I'd clean it out occasionally and not worry about it, but that's me. Some here might even consider it normal...but worth checking out.
 

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1998 750 ACE
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Yeah, this is typical of our Bikes to have a little bit of oil in there...Look at that clear "pinch valve" (drain hose) to be sure it isn`t blocked...
Mine is still welded shut though...;)
 

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I`ve read here, that this oil in there is caused from crankcase breathing...
IF you run hard, it gets worse than if you "Granny ride" :D

Mine always has some ;)
 

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I`ve read here, that this oil in there is caused from crankcase breathing...
IF you run hard, it gets worse than if you "Granny ride" :D

Mine always has some ;)
Hey Dennis, I agree and why I said make sure your "crankcase breather system is up to snuff". There is a catch tank for the crankcase oil vapors on our bikes that is supposed to trap most of that, but I agree if you get on it hard oil vapors might pass through to the air box (no time to settle :)). Bottom line is get on it hard, have fun, and clean up after you are done. Wow, that sounds a bit like good sex. LOL
 

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Its designed to collect the oil from the positive crankcase breather system. Just like your car and its PCV valve.

Also theres nothing that says you cant pull those hoses off the air box and run the hoses vertical so they dont leak on you but allowing the crankcase to still breathe.
 

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Normal.

Like said its the crank case breather, its routed into the air box for EPA reasons. Bound to get a little more in the air box if you run the bike hard (hotter oil temps, needs room to expand) or have slightly over filled the crank case with oil. either way there should be a little tiny plastic bag clamped on to the air box as a collection point for this oil. Empty it out every oil change or so.

Ideally one would route the crank case vent into the atmosphere and keep the oil gunk from going into your intake and cylinders. I put a stage 1 intake with crank case breathers that vent into the atmosphere on my bike, and with only 4500mi on the bike and the stock intake I had a nasty black gunk coating the inside of my throttle body from the crank case breather set up in the stock air box. Also I've seen engine tear down pics from bikes with less than 10,000mi with and without the stock air boxes, and the ones with stock air boxes that have crank vents into the airbox always have much more build up on the pistons.
 
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