I have two 2005 Yamaha Bruin 350 4x4s. They have about 30 hours on them and have gone through the first dealer checkup after 20 hours. Both are behaving the same way. I have not seen this problem since the 20 hour checkup when the air filter was re-oiled.

The air filter (seems to be oil imprenated foam) is in an enclosed box under the seat. On the top of the box is a throated opening which goes further up under the gas tank cover. On this throat there are three small rubber tubes that: (1) connect to the rear drum brake, (2) connect to the rear end, and (3) looks like it connects to a vacuum advance or something on the engine. After running the engine for a few hours, I notice that at the top of the air filter throat, there is a slight amount of oil that dribbles down the throat side onto the sides of the air filter box and then down to the engine. No oil seems to be coming out of the rubber tubes. It is just a slight amount of oil; but, enough to be annoying.

Any idea what the cause of this slight oil accumulation is ? I am wondering if it is just the oil imprenated air filter "out gassing" when the throttle slows down.

Thanks

 

I have the same problem myself with the oil filter leak, just a small amount. I have about 150 hrs on mine and it hasn't really been a problem, more of a annoyance.

 

I just found someone else with this problem in another chat room. They were told that the rubber tubing that air vents to the rear end is the probable culprit. Sounds weird; but, there isn't a whole lot of places the (slight) oil leak could be coming from. I'm going to look closer at the end of this air vent to see if the oil is coming from there.

 

Hi, let me know how you come out. If I hear anything on this end of the world I'll let you know.

 

I just took my Bruin to the dealer. As it turns out, the "leak" is the differential gear oil venting out of the vent hose. They put a something like a filter (ie, a gas filter with no filter material) right at the differential inline with the vent hose. The "globe" will catch the venting oil and let it condense back into the differential. They did this for both the front and rear differential.

They said the problem is worse in cold weather.