Oil in Air Cleaner Box


New Member
First as you can tell I'm new...so howdy all. :)

1993 Yamaha Utility buggy it has aluminum dump bed with removable sides and tailgate. I bought it from a local golf course about 7 yrs ago. I've noticed it's getting oil in the air cleaner box.

It has ran like new ever since I have had it.

I put a 7" lift, ITP wheels and oversized tires, clutch, spring and inner flywheel for the gearing change, recovered one of the back rests, camo painted and made dash doors for it.

As I stated earlier, it has always ran great. Parked it last fall and went to start it last week and it would only turn over and not hit. Good fire-check, drained old gas and changed fuel filter-check, fuel pump-check, carb not picking up gas from bowl seemed to be the problem. Took carb off and apart, cleaned it and reinstalled-still won't start? I could put my hand over the carb where airbox hose attaches for a couple of seconds while turning it over and when I would remove my hand it would run-till it used up that little bit of gas. So I removed carb and recleaned, reinstalled-it runs!

But when I hooked the airbox hose back up it would not run? And that is just the hose not attached to the airbox. I left it off and drove it down tthe driveway-ran great. Coming back it ran like it was straining and running very slow. I raised the bed and my airbox was half full of oil?

Started checking the lines coming out of the valve cover, there are 3, and there is a short L shaped hose with a check valve in it that tees into the fuel pump line. The check valve had came apart.

Is that why it is pumping oil into the airbox?

And the carb problem...I just figured it needs a rebuild kit.

Also checked compression it was 150 and the engine does not smoke.


The check valve is like a PCV valve (Yamaha calls it a Vacuum Control Valve) and it will cause oil to get into the air box if it's not working. Did the oil start getting in the air box after you installed the lift kit? If so it may be over full of oil.