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What many don't think about, we all understand what our piston does on the compression stroke, forcing that air and fuel into a tiny space just before it ignites and starts the fun.
But on the down strike, that piston increases pressure underneath it, in the same way, but in the crankcase. The air volume, in the crankcase absorbs some of this along with the other piston now going up on the compression stroke. But if there's too much pressure, air is forced out of the breather relieving that pressure. If there's too much oil and not enough air volume to absorb this compression, some of that over fill of oil goes out the breather as well along with some air.
The higher volume of oil also means where the oil is frothed up, more is suspended, like spray from an ocean wave, and this is pushed out the breather into the airbox where it re-condenses as oil.
But on the down strike, that piston increases pressure underneath it, in the same way, but in the crankcase. The air volume, in the crankcase absorbs some of this along with the other piston now going up on the compression stroke. But if there's too much pressure, air is forced out of the breather relieving that pressure. If there's too much oil and not enough air volume to absorb this compression, some of that over fill of oil goes out the breather as well along with some air.
The higher volume of oil also means where the oil is frothed up, more is suspended, like spray from an ocean wave, and this is pushed out the breather into the airbox where it re-condenses as oil.
jarelj
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Check inside the airbox and see if the breather tube popped off of the fitting down in the bottom left side of the airbox next the throttle bodies. It's secured with one of those little clip-style hose clamps and I've seen them blow off if the oil level is a little overfilled and then it just vents oil into the airbox from that point on and no amount of draining the oil will fix it. You'll see oil dripping out of the vent tube at the bottom. I chased this problem down on my bike at a track day at COTA this spring, and this ended up being the cause. We replaced the clamp with a worm drive clamp so it will never come off again. After the fact I learned this was a common issue with many of the race teams.
jarelj
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It's a "Worm Drive" or "Worm Gear" hose clamp, it refers to the tightening mechanism of the clamp. Like this:
General Purpose Hose Clamp - King Seal
Much tighter and more secure than a clip-style hose clamp, like this:
http://www.autohausaz.com/search/product.aspx?partnumber=32411712735&utm_source=google&utm_medium=nonpaid&utm_campaign=frooglePN&utm_term=32411712735&gclid=CNyPktiuoc4CFQgOaQodx6oPCA
The breather rubber hose, the conical one coming down from the airbox base, tends to split with heat from the motor. This was reinforced with the later 1199's, and the 1299, but I've still seen them fall apart. The hose clamp is also a clip-fit one, and a proper worm-drive clamp is better. I cut the breather tube back, place an alloy insert into the upper bit and relay it to a heavy-duty heat and fuel resistant rubber hose clamped onto the motor breather spigot. No more problems.
To resurrect an older thread for a minute....
I am changing air filter and in the airbox I noticed oil in the bottom left side (left leg side) and a little in the vent tube down to the bottom of the bike. It was the breather hose that popped off. The clamp looked good. I shoved it back down hard and I will monitor it. If it pops off again, I will worm clamp it like Jarel suggested.
When you have your tank off and access to the airbox, take a second to look at the fat black hose on the left side closest to the vertical head to see if its got any movement or oily residue.
Just a heads up.
NOLA
I am changing air filter and in the airbox I noticed oil in the bottom left side (left leg side) and a little in the vent tube down to the bottom of the bike. It was the breather hose that popped off. The clamp looked good. I shoved it back down hard and I will monitor it. If it pops off again, I will worm clamp it like Jarel suggested.
When you have your tank off and access to the airbox, take a second to look at the fat black hose on the left side closest to the vertical head to see if its got any movement or oily residue.
Just a heads up.
NOLA
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