ACV mods.

What is the best way to totally disable the air cut valve? I have plugged small hole, and cut the pin on the diaphram, removed the spring. This helped, but not completely. Also thought about using silicone, could get messy! Bike is 2000 WR400 yz timed, DSP exhaust, EKN#4 MJ170,PJ42,PAS65,MAJ160,AIR SCREW 2.0 rich on bottom, lean reading on top, cr8eix. ACV seems to mess up jetting more on bottom. :)

Awwh man, all you needed to do was flip it over. Since you've gone that far, I don't have any other suggestions........sorry.


Dodger :):D

Yep i could do with some good info on the acv mod too(for an 01-426)would like to know the best way to do this so i can easy change it back if i`m not happy with it!

atk450, I would think your bike would probably be rich because you are using a 170 main jet and only a 160 main air jet. Most guys with a 160 maj are running main jets in the 150-160 region. The guys using the fatter 168-172 type of jetting are usually using the 200 main airjet.

Why do you need to disable the acv anyway? What kind of poor running symtoms are you tryin to fix? Maybe its a jetting problem and not the acv.

just my thuoghts!

I've heard the ACV has a way of throwing your jetting out of whack on decel, I think this is when the ACV comes into play, but not positive.

At any rate, I've changed to YZ timing and jetting, and can't understand why I wouldn't flip my diaphram around and disable the ACV since YZ's don't even have the option.

I really havn't felt much difference before vs. after. But my bike runs good....sooooo.


Dodger :D:)

I know what you're saying about disableing it dodger, alot of people do it, The acv cuts off the air coming in the pilot air jet on decel. This richens up the mixture and prevents any popping in the exhaust.

If atk450 has plugged his hole and cut things off and taken out his spring etc and is still having problems the acv probably isnt the cause of them.

I still think that 170 main jet should be run with a 200 main air jet and not the 160. If I put those jets in my bike I know it would backfire and run like a blubbering fat pig. Been there done that!

ATK450, can you give us any other symptoms of what your bike is doing and when.

hope this helps.

Thanks for your replys, forgot to mention bike is BK'd .5 sec. I'm trying to eliminate anything that interferes with getting fine crisp tuning. I guess it's more an issue of getting the jetting correct. With my above stated carb settings, and full throttle run and ignition chop my cr8e and cr8eix show black ring at thtreads, and white insulator with electrode light gray. feels like it's starving on top. I've tried emm #4 165 mj,160maj,55pas,38pj,2.0a.s. plug showed lean white insulator light electrode. You wouldn't think with that main jet it would be lean. Ran quick but, cut out like hitting rev limit in all gears. It was like engine wasn't revving out all the way, more like cutting out sooner.

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