Oil in the air box of my 76 kz900

My kz900 is in great shape. All original except for the LTD pipes. It runs awesome and I ride it regularly.

Yesterday I took a ride for coffee with some other classic bike guys. When I got home I backed the bike into the garage and put it in the side stand (no centre stand). This morning when I went out there was a puddle of oil beneath the left side chain adjuster. The oil had run out of the air box drain, down onto the swing arm, then run along the left side swing arm and dripped off the end. It was a significant puddle.

What would cause the oil to be forced up into the air box? The crank case oil was definitely NOT over full. The oil level is now half way between the marks at the sight window.

Cheers,
Ross

At high RPMs these bikes blow oil out of the crankcase vent into the airbox. I don't think I've ever had oil drip out of the airbox, but I'll pull my filter and wipe down the inside occasionally, there's always a little oil in there (good for catching dust and crap).

Just guessing -- perhaps gasoline had for whatever reason entered the air box, and diluted some accumulated oil residue, and the nasty thin mixture drained from the air box.

Meanwhile, would sniff-test the crankcase oil and examine it to determine whether there might be fuel contamination of the oil.

Good Fortune!

No gasoline smell in the oil. Out of habit, I always turn off the petcock when I turn off the engine.

The amount of oil on the garage floor, is about how much would flood the floor of the air box without contaminating the air filter, which was clean and dry. The oil in the air box, on the swing arm, and on the floor is good clean oil.

I often do a redline run up through 3rd or 4th gear after the bike is warm, and I've never had this happen before.

Ross

your crank case oil vented and is no big deal...there are dozen reasons why it does it and that is dif for every rider type by a bit times that dozen imo....

cold days and not spot on timing or pulling a grade ....carbs off... and so on ..nothing too big to worry about...now if unnoticed , and one day it built up and got on the tire....makes for a fun first corner after a good long straight section, gets everything dirty too if it drips in the no pressure area under the box and blows around.....

too much oil by a half cup or more is the number one reason...pull some heavy revs it will come out for sure

Thanks Tri,

I had decided that it wasn't a real big issue at this point. I cleaned everything up so I can monitor it closely. The oil level is still good, so it must not have puked out very much.

Interesting that you mentioned cold weather. The temperature when I was riding was 2C, about 34F. I wouldn't think that would be an issue. I've ridden in much colder weather.

Thanks guys, I'll keep a close eye on it from now on.

Cheers,
Ross

In that cold of weather, the engine will operate colder. This will cause more clearances in engine parts, mostly the piston to bore/ ring end gaps. So a bit more blow by when you did your Tach Test. If it continues in warmer weather/ operating temps, then it may be a concern. Leak Down Test is where I would go, THEN.

you have an eye for bike on the country shots...cant wait to see some more pics when you get time
Craig

Make sure the oil in the crank case doesn't smell like gasoline as well. Just in case