1999 Kawasaki Vulcan 800 Oil Gushing Out Through Air Filter

I have a 1999 Kawasaki Vulcan 800 Classic, when I start it up, oil starts pouring out through the air cleaner after a few seconds. I removed  the cover and noticed the oil is coming from an air breahter hose attached to the air cleaner housing.  I also realized the clutch is not working.  There is way too much slack on the cable as if the cable has all of a sudden stretched, but I think these two incidents are related.   The oil breather hose attaches between the air cleaner housing and the rear cylinder.  the bike only has 1500 miles so i hope this is not a major engine problem, what a bummer this is, right before summer is starting.

Hey Taprado –

Oil coming out the crank case vent has two very common causes, and a couple not so common ones. The most typical cause is the bike being overfilled with oil. Have you checked your oil level according to the factory procedure for your bike?

If the bike has been sitting it is not uncommon for the carbs to be gummed up allowing fuel to leak into the cylinders and mix with the oil. Does the oil smell like gas? Is it thin?

If the oil level is fine and it’s gas free then you likely have a more serious issue. Extra crankcase pressure builds up when the cylinders are having blow-by. A stuck (or broken) ring can cause enough  blow-by to spew quite a bit of oil.

Additionally it could be the breather check valve being stuck open. This isn’t too common and likely isn’t easy to check on your bike (however some bikes are easier than others).

First things first. Check the oil level. Inspect the oil quality. Report back.


the oil smells like gas, actually i thought it was gas coming out until I realized it is oil and now that you have pointed it out it is gas and oil mixed together.  I was in sunny Iraq for almost a year and the bike sat for sometime before I had it serviced.  I had them replace the oil but they didnt do anything to the carb.  That’s why it’s better to learn how to do these things yourself.

Well we got to the bottom of that pretty quick!

Time to pull your carbs and give them a good cleaning. If the bike is running OK then you likely just have a sticky float or a dirty float needle.

Also make sure you flush out all the tainted oil.

No problem taprado, happy to help.

Gas in the oil can cause the clutch to slip, but it wouldn’t create slack in the cable.  Check the clutch cable adjustment at the perch and at the motor and adjust as much slack out of it as you can. If it was working fine before it should still be working fine after a year of sitting.

well I am not sure what I did wrong but I am back to square one.  The cranckcase is full of gas again and at one point the engine was in vapor lock so I pulled the plugs out and cranked the engine over to get all the vapor out of the cylinder and the rear cylinder was shooting the gas/oil mixture straight out the spark plug opening.  not sure where to go from here????  is it still the carb that is bad??? did I miss something when I cleaned it?????

If you are getting oil out from the rear cylinder spark plug hole then you have bigger problems. You probably have a broken piston ring.

The gas can only get in the oil under 2 conditions – running, or non-running.

If the bike sits it may still be dripping gas out through the rear carb and into the cylinder. I would monitor this very closely by removing the fuel hose from the petcock and watching if the fuel in the hose disappears as it drains downward. It should stay at the same level.

If gas is getting in there when running then your cylinder is damaged.

First things first – put a compression gauge on the cylinders and report back with what PSI you get.

A cheap compression gauge can be purchased at Harbor Freight for around $15.

compression is 115 in both cylinders.  i wonder if i did not get all the gas out of the crankcase even after i change the oil th first time.  i put some regular cheap oil in and rode it for a little bit, now i am draining it again and am letting it drain for several dasys to make sure it dries out well.  clutch sure is acting strange, having a hard time getting it in first when i stop.

Evan Fell

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