ACV.....Proper way to close it off ??

8 replies to this topic
  • rekless

Posted July 14, 2004 - 08:00 AM


YOu guys that have closed off the ACV, what method did you use? I have heard pull the diaphragm out, or turn it around, or just seal the hole up???? Can someone shed some light on what worked for them? Thanks yall, rekless :thumbsup:

  • ogrebelle

Posted July 14, 2004 - 09:48 AM


Just flip the diaphram over (it'll make sense when you do it) and call it good. :thumbsup:

  • mtrablue

Posted July 14, 2004 - 01:12 PM


i just flipped the diaphram over. be sure to leave the spring out.

  • rekless

Posted July 14, 2004 - 01:17 PM


Okey Dokey !! Thanks, rekless :thumbsup:

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • 5spoke

Posted July 14, 2004 - 02:33 PM


Check this thread:


Air cut Valve training 101-

The Air Cut Valve (ACV) lets extra air flow to the pilot jet during most running conditions, but not under deceleration.

The carb has 2 air passages to the pilot jet and one (the ACV passage) closes of during deceleration. This richens the pilot circuit on deceleration to reduce popping. The Air Cut Valve "Cuts" the air passage off by using vacuum to pull opposite the spring and diaphram.

Pull off the cover.
--The center hole with white plastic valve leads directly to the pilot jet air circuit, along with the pilot air jet. The diaphram spring and pin normally hold the valve open.
--The hole on the left leads straight into the intake manifold for vacuum. This pulls the diaphram pin away from the center hole on deceleration, closing it.
--The hole on the right leads to the airbox side of the slide. It allows atmospheric pressure air to flow thru the passage in the center when the vacuum is lower, and leans the pilot circuit. The WR's have a bigger pilot jet(42-45) than the YZ's(40-42) to compensate for the added air.

The ACV simply cuts the air to the pilot jet in half when using engine braking.

If you disable the ACV with the center hole closed, the pilot circuit will run richer both at idle and on deceleration. If the center hole remains open, the pilot circuit will be leaner under the same conditions.

Got it?


So this is what I concluded from JD's post:

If you leave the diaphram plunger in the 'in' position (sticking into the white plastic thing), and you disable the vacuum or make a spacer to hold the diaphram plunger 'in', you don't have to change the pilot jet.

If you leave the plunger out or swing the diaphram plunger around, you need to change the pilot jet to #40-42.

Hope this is right. :thumbsup:

  • RichBaker

Posted July 14, 2004 - 02:44 PM


You got it, 5spoke.... :thumbsup:

  • rekless

Posted July 14, 2004 - 05:49 PM


I think I got it. What I might try is making the spacer out of a short piece of rubber tubing. Does that sound like it might work? What did you use? Or did you just switch jets? I did this all at the same time as the TPS. WHEW!! What a difference. Thanks alot guys. rekless :thumbsup: :devil: :awww:

  • Hamish

Posted July 15, 2004 - 01:42 AM


ok..stupid question time. What advantage does disableing the ACV have?

  • djrevz

Posted June 22, 2010 - 10:14 AM


Posted Image

This im confused about, i have been thinking of doing the grey wire mod but as i started to do it i realised the grey wire wasn't even connected in the loom apart from were it goes in the cdi. i striped the wiring to see if i could find the grey wire further in the loom but nothing at all.... my wr 426 is a 2002 model the picture above is were the grey wire feeds any thoughts on whats going on here?


Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.