I have a 2001 rancher 350 es, started to run bad so i replaced the spark plug and was checking the air filter when i notice a lot of oil in the bottom of the air filter housing. Any ideas on what is causing it and how do i fix it.

 

It seems like this question comes up from time to time. The air filter has oil sprayed into it. The oil might be from the filter. Is there a puddle of oil or is the bottom of the box just wet with oil?

 

When you take your air filter off, you will notice a little square housing (like 1 inch square) that the filter rests against. This is the vent from the crankcase, and you will notice that a tube runs from it to the engine (the housing itself has a little sponge filter in it). If your air filter is really dirty, it is very easy to see where the housing rests against the air filter, because that spot will be clean. Anyway, sometimes during rough high speed riding, oil gets sucked up from the engine, through the vent.

It happens in all bikes. It is just that in the Hondas that put the vent against the filter (not all models do this), oil will saturate the filter and the extra oil drains from the filter into the bottom of the airbox, when the bike is sitting. The Rancher is particularly bad in this respect, and I don't see why Honda can't build in a baffle in the engine that would help prevent this. I have never noticed that it affected the bikes performance though. It is just a pain to clean up that oily airbox.

 

I think there is at least one official Honda bulletin dealing with this. A very few (I've never seen one) had flaws in the cases causing oil to literally run into your airbox. Also too thick, or too much oil will end up in your airbox. Being a dry sump engine, Oil level is critical and you MUST check the level according to manual. I've also had that little square foam (the one the reconranger is referring too) freeze up in the winter several times, allowing the cases to pressurize and blow oil into the airbox.