Someone please explain function of the valve cover breather hose

26 replies to this topic
  • dangermouse007

Posted January 10, 2005 - 12:48 AM


I for sure will be changing mine.... Went into Deep water this weekend, and the Engine Just died, pulled it out with out starting... but what a crap design.....

This may help you Re-route

  • stumpyten

Posted January 10, 2005 - 02:53 AM


I carried out the same mod as wr Dave on my 99wr 400 about a year ago and ive never had a problem.i trail ride a couple times a week on routes with plenty of river crossings

  • stumpyten

Posted January 10, 2005 - 03:03 AM


Iwould like to add to my post above that stalling or cutting the engine in water will cause suction on an unmodified breather due to the rapid cooling affect of the water

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  • moto_dyll

Posted January 13, 2005 - 10:25 AM


I agree moving the breather hose is a good idea for yet another reason, I was trail riding through some pretty difficult hills and put my bike on its side the breather hose slid back and pinched itself i picked up the bike didn't notice anythig and then a while later doing another hill climb i blew my cam cover and was done riding for the day

  • Guy

Posted January 14, 2005 - 03:36 PM


About :

Could you show us a picture of the factory set up ?

I wonder why Yamaha didn't standardise this set up ?
I beleive that water crossing in America is about the same as water crossing in Europe. :cry:

So why the difference ? :cry:

its only available in the street legal kit not as stock on the euro/uk WR's.,,

this subject is quite an old one and has been done to death a few times !:cry:
the general consensus last time was that just routing the hose to the airbox wasnt that good as all the white goo you get from collects in the box !

as someone here has already mentioned a small T section approx 1 " down the hose (so ALL the smeg will drop out of the hose !) then a secondry hose routed to the airbox, will ensure that there is NO suck back as when the lower hose is submerged it will suck from the upper.... and if the upper hose is submerged..... you is in the Pooh !:cry:

the PCV valve was also discussed at length at I seem to recall that the opinion was expressed the the engine needs to "suck " as well as "blow" so it would in fact create negative air pressure in the crankcases.not ness a good thing !:cry:

  • Beef

Posted January 20, 2005 - 04:33 PM


I just checked out the new '05 WR's, and it looks like they fixed this problem. As far as I can tell, the PCV now goes into the bottom of the airbox. :cry:

  • unkle_george

Posted January 20, 2005 - 05:41 PM


Yamaha made the hose long enough to hold the complete volume of air the piston displaces. Then you're just moving the same air in and out of the hose ... clean air in theory.
I've cut mine down some too just so I won't accidenly kink the end of it shut.
Hmm, you could replace the hose with a balloon... : )


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