Air Cut valve

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

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.


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.

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


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.


i did mine

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

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now