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Jackazz

Disabling your air cut-off valve

11 posts in this topic

Who's done it, & what do you think of it? Just trying to figure out what mods/upgrades I'll be doing this winter when the "holiday" schedule prohibits me from riding on the weekends.

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That's the logic I'm working from as well. I was just hoping to get some "real" opinions on it from people on here who've done it instead of 10 people sending me to the wr250/thumperFAQ page, which I've allready read. I did note that the ZY carb comes with a #42 pilot jet, while the WR comes with a larger #45. TT member MTRABlue commented that he thought it was due to the WR having the ACV.

I know it's a fairly easy & reversable mod, I'd just rather spend more of my riding time riding than tuning, due to the limited amount I get in.

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Although I haven´t tried it either I am interested too. Perhaps this is no news, but the function of the valve is to let the combustion mixture richer when you shut-off the accelerator before you enter the corner. The YZ´s typically give the popping sound in the pipe (back firing) this is due to a too poor mixture, which your bike doesn´t like. The downside of the cut off valve is that it leaves the bike (too rich) when you hit the gas, exitting the corner, leaving the bike less responsive. Perhaps general enduro purposes, the engineers thought it would be better to let the WR run a bit richer, reducing the chance that the bike kills when you suddenly open the gas of idle. I just order today my YZ cam, (anyone) do I need new shimms to adjust valve clearance?

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That's the logic I'm working from as well. I was just hoping to get some "real" opinions on it from people on here who've done it instead of 10 people sending me to the wr250/thumperFAQ page, which I've allready read. I did note that the ZY carb comes with a #42 pilot jet, while the WR comes with a larger #45. TT member MTRABlue commented that he thought it was due to the WR having the ACV.

I know it's a fairly easy & reversable mod, I'd just rather spend more of my riding time riding than tuning, due to the limited amount I get in.

Ditto, that's why I love this site so much because there is so much "real world" info here. Thank you!!! :cry:

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I am confused. Are you discussing the AIS valve that is new to the 05'S. I have removed mine and I am in the process of having the pipe cut and welded shut.

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I removed it from both my 426 & 450. Makes sorting out the low speed jetting a little more straightforward. BTW the YZ has a 42 pilot because it also has a 100 pilot air jet instead of the 70 used in the WR. Generally it's a little more crisp coming off of idle.

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i did it for a while. there was no real performance gain. if anything it made jetting more difficult for me. i was changing over to the 100 pilot air jet and the 40 leak jet. then add trying to figure out if i needed a 40 or 42 pilot jet had me going in circles. i put the acv back to stock and threw in the 48 pilot jet and i'm a happy boy.

there's no reason not to try it. take off the little cover. remove the spring. turn the diaphragm around. put the cover back on. leave the little o-ring where it is. change your pilot jet. there seemed to be ten differant opinions on the best way to disable it, but that's the easiest. have fun.

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You are right I was referring to the valve on the left side on the carb, not any of the new stuff on the 2005 model ,ieeee!

Robert

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Is this something that can be done to a 02 WR426? After 2 1/2 years I still have a slight bog and foul plugs too frequently. Benifits?

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I closed off my ACV to get rid of the irritating stutter when I hold the throttle steady, like on a road transition from trail to trail.

It did get rid of the stumbling at even throttle, but as for other performance gains there was nothing noticable.

There is a slight backfire when you decel into corners from high rpms, but with the help of JD jetting , it runs great with no hesitation anywhere.

I also disconnected the TPS, but reconnected it after I felt I lost a little low end.

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