Compression release valve

10 replies to this topic
  • Jeff_Nyfeler

Posted May 24, 2004 - 08:48 AM


I have a 2000 YZ 426F that I let my buddy ride the other day. As he slowly rode off, I noticed dust kicking up from the ground directly underneath the foot pegs. Upon closer inspection, I observed that when the bike is running, exhaust gas flows through the rubber tube -- the tube that acts as an exhaust tube for the compression relase valve. Now, I understand that gas should come out of this tube when the compression release lever is pulled and the kick start is kicked, but should it happen when the bike is runnning? Is the compression release valve one of the two exhaust valves or is it a dedicated valve?

  • Oasis_Flame

Posted May 24, 2004 - 10:17 AM


Ah, Nope. The compression is released into the headpipe using the right front exhaust valve. You may want to take a closer look at beast, things aren't sounding good. :thumbsup:

  • tp3dxf

Posted May 24, 2004 - 10:39 AM


Sounds to me like the black rubber tube that comes off the top of the cylinder I believe. On my WR it routes off the to front left side of the bike and exits near the shifter. I believe it's some kind of vent for the motor. Mine spits out a little oil after each ride. Unless it's really excessive sounds normal to me.

  • Jeff_Nyfeler

Posted May 24, 2004 - 10:53 AM


Thanks, guys. I'll take a closer look when I get home today.

  • Rich_in_Orlando

Posted May 24, 2004 - 03:20 PM


It's totally normal. Don't worry about it. It's the crankcase breather tube. Just make sure that if you stall in deep water, don't kick start it if the tube is under water or it might suck water into the engine.

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  • dirtstiff

Posted May 24, 2004 - 05:04 PM


You will also notice oil will come out of the vent tube once you get the bike off of you and turned back right side up... :thumbsup:

  • Jeff_Nyfeler

Posted May 24, 2004 - 06:03 PM


Thanks Rich. I looked closer this evening and I see that the tube comes out of the top of the valve cover. Glad to hear that what I observed is expected.


  • SteadyEddy

Posted May 24, 2004 - 06:18 PM


hey Jeff, check out this website, they moved the hose into the air filter box....
I wonder what would happen if the oil went back through the carb :thumbsup:

  • The_Missile

Posted May 25, 2004 - 06:04 AM


please please please dont start that topic again !!!! :thumbsup:

  • SteadyEddy

Posted May 25, 2004 - 12:02 PM


ok, but what should i search for to check out old post's on this subject :thumbsup:

  • SteadyEddy

Posted May 26, 2004 - 02:29 AM


not to worry,
found the info :thumbsup:


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