wr450 air cut valve

Has anybody disabled the air cut valve on the carb?


This crops up now and again. There was a post some months back re. TPS and Jetting. There is some ground covered there.

I suggest you look in :


This will give you an in depth understanding.

It helps to understand what the ACV is there for..Basically in the closed position (ACV closed) it prevents some air flowing to the pilot jet/circuit, hence richening the mixture. This closed position occurs when the vacuum differential is such that it pulls against the diaphram and closes the ACvalve. This should occur when the throttle is closed - ideally on decel; and is there to aid lean conditon and alleviate popping- on some bikes and cars it is called a "coast enricher" or CE. When in the open positon (normal, diaphram pushed in by spring), all the air is allowed to the ACV via the PAJ, hence the pilot circuit is leaner. This should occur under normal "on-power" throttle settings.

There are many variations listed in FAQ but they achieve either:

1. Disable it in the OPEN "Normal" position

2. Or Block it in the CLOSED position

The end is the same only you have to rejet the pilot to smaller (say from 48 to 42) AND chnage out the PAJ (in the intake bell) to compensate.

What I found:

My ACV was interfering with the low throttle on/off mixture and making the fuel screw insensitive and I felt the engine was "running on" a little, BUT I had no pops on decel - that is what it is for.

I disabled mine OPEN, thus leaving the jetting alone.

The fuel screw now works as advertised AND the bike (I think) is easier to jet by hearing ie. no artificial interference from the ACV. My bike does now pop a little on decel, this I can dial out with 1/4 fuel screw but that makes it a little rich off the bottom. SO, I leave it and accept a little popping.

I posted a similar Q in jetting some months back to find the preferred method. Either method is OK, you just have to adjust your PJ and PAJ if you block the ACV or close it off!


I think I got that all right? :crazy:

Great info :crazy:

Thanks! Yes, that is what my '06 is doing.."running on" after the throttle is closed.

TT is awesome.

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