I have a Yamaha WR426F that after a bit of trailing has a small (couple drops) puddle of oil underneath it after sitting a bit. It seems to be coming from the breather tube, is that normal?

I also have a title with the bike that has it described as an enduro does it mean that it is street legal? It has brake light, mirror and horn. The state is Illinois. Sorry if the last question is not suited for this category just don't know where to ask.

  • I got a registration for a Honda crf230f in Illinois. I added a light kit, even got it inspected at a police station and got a letter. DMV didn't care. Just gave me a plate no questions asked.
    – cory
    Jul 25, 2016 at 17:23
  • Thank you! Called the DMV and they didnt even care as long as I had a title, very excited to drive on street but the oil issue is still there. Jul 26, 2016 at 15:49
  • What is the breather tube connected to? Is it's source the airbox, fuel tank, etc? Aug 1, 2016 at 20:47
  • Do you have a source for where the breather tube is connected to. There are a few. Aug 12, 2016 at 19:46
  • Is the breather tube connected to your airbox? Aug 31, 2016 at 18:38

2 Answers 2


You may have a bad PCV valve or your rings are getting worn out

Your PCV valve controls pressure within the crankcase and assists in dispensing excess oil and running it through the engine as well as ensuring that an excess of internal pressure in the crankcase has no negative effect on your crank and transmission seals.

It is normal for the crankcase ventilation to put oil in your airbox IF you have a condition that would explain this.

Check the following items

  • PCV valve - ensure it's functioning properly. You have a reed valve type and the reeds should be in the closed position when not in use.

  • Rings - if your rings are bad you will be getting too much positive crankcase pressure from exhaust gasses blowing by the rings into the crankcase. You can test this using a leakdown test.

  • Too much oil - if you have too much oil in your crankcase it's very common to see that oil showing up in your airbox and fouling up your air cleaner. Make sure the bike is vertical when you check your oil level. If you have too much oil, drain a bit out so that it's at factory recommended levels.

If you require guidance on howto perform a leak down test, here are some instructions.


You're talking about the crankcase breather? A couple drops doesn’t sound that unusual. There's oil mist inside the crankcase and it can condense. Often times folks will route the crankcase breather tube into a catch bottle for that reason.

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