Air Cut valve

6 replies to this topic
  • Guest_Guest_*

Posted February 16, 2000 - 08:19 PM


I just picked up a 99 wr400 from a 67 year old ( A bit to much torque on the torso). Any way he handed me the air flilter cover, the exhaust baffle and the air cut valve assembly off the side of the carb. He said that the mechanic at the dealership took them off when he picked the bike up. The baffle and air filter cover are well accepted helps but why the air cut valve ? The bike runs well but I don't have anything to compare to. Should I put the thing back on ? Thanks Sparky

  • Clark_Mason

Posted February 16, 2000 - 08:45 PM


The air cut valve is what we have been refering to as the octopus on the left side of the WR Carburetor. If you properly plug/cap the the #2 air start jet and the connection on the carb input air horn
should be ok. I also rejetted. I believe other forum users have also removed this not vital piece. If you search the archive and use the keyword "octopus" you will come across one of my posts which explains, in detail, how to remove the octopus and rejet the carb.


  • Guest_Guest_*

Posted February 16, 2000 - 10:09 PM


Thanks Clark I pulled your old posts and will check things out. Considering the octopus is already off I wonder if the dealer mechanic dude made any changes to the pilot air jet or the start jet ? I also have not checked to see if the throttle restrictor has been shortened.

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  • Dougie

Posted February 16, 2000 - 10:35 PM


Clark, your post won't come up when you search "octopus". It is in the first archive and the post is dated Oct. 24 and titled "Re: Factory jetting for YZ400?--Eliminate Vacuum module".

After I pulled my carb, this octopus did not go back on in the same postion. So I am thinking of removing it. In your post you say to change to a #100 pilot air jet and a #65 start jet. Does that also go for us up in altitude in CO that are YZ timed? I assume the blocking caps can be picked up at any automotive store. Are they all the same size or do I request a certain size?

Dougie, '99 WR400
Mods: Race Tech Suspension, YZ Timing, FMF PC IV, FMF Hi FLo Moto, YZ seat, IMS 3.3 tank, One Industries Graphics

  • Clark_Mason

Posted February 17, 2000 - 06:17 PM



If you continue to ride above 6000 feet you might try changing the air jet to a 100 and leave the stock start jet (#60) in place. But I would definately change to the 100 air jet.

You can usually just pick up a set of assorted sized vacuum port blocking caps and just use the ones which have a nice snug fit. I got some multicolored rubbery vinal ones at I think Kragen but any well stocked auto parts store will have them. The larger caps are great to put over the firing end of a spare spark plug for throwing in the fanny pack.


  • cj_wai

Posted January 25, 2010 - 05:44 PM


i did mine

  • William1

Posted January 26, 2010 - 02:29 AM


10 year old dead thread... revived - Geez!


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