Air cut valve (need info on this mod)

Need info on what the air cut valve mod will do.have been trying some set ups on the carb and i think i`m still a bit rich,the bike is sound when i`m on the gas from low down to full throttle,but when i shut of from high rpm and let it run back down under its own engine braking,when it comes down close to the pc range it sounds a bit fluffy,is this down too the acv,as i am under the impression that the acv is there too supply a little extra fuel under decel.Can any of you guys tell me the best way too do the mod,and what you found before and after doing it,i am now running the bike with emn neddle,i`m also under the impression that yz`s dont have the acv`s fitted,so if i`m running the e-series needle should the acv be imobilised!,any help would be great cheers.

The ACV enrich the mixture when deceleration. Lot's of people disable it(including me) so that we can fine tune jetting. There are a couple of ways to disable it. I personally removed all the stiff and put some rubber to the small and the big hole. Some guys just flip over the membrane, but there ware discussions about not completely disabled ACV. Make a search on ACV mod and you will find a lot of info. I also remember that you may have to make some minor changes in PC, but not sure what changes.

what year is your bike?

Ok guys here`s where i`m at,bike is 01-wr 426 euro spec,lid off fmf Q-pipe,168 main,170 maj,emn#3,35pj,55 pas,the bike does run well rite through the rev range,when i take it to flat out in top and let it coast back down under it`s own engine braking when the revs come rite down i can hear it make a deep sounding kind of warble,not a sharp crackle like it would if it was lean,now if i take the mixture screw out a little it helps to make it go away(but i think this may be because i`m making it just a little too rich to do it)have tried the bike with a 165 mj but it seem make the revs hang up a little when coming back down to idle,(again i can help this by turning the ps out to near 2 turns) and i do think i have a little better top end with the 168,although i do have a 165 maj i can try with the 165 mj,i would just like to now the best way too try the acv mod so that i can easy change it back if im not too sure with the result,i`m just trying to zero in between the 165-168 mj`s,any info you guys have from before and after this mod would be great.Did try the search but didn`t really find what i was looking for(maybe it was just me!). Thank you both for your replys i value your help greatly,2-years i`ve been fettling this puppy an i think i`m almost there!

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