2003 WR450 2005 YZ450 carb

I needed a carb for by WR after it spent some time under salt water after hurricane Ike. I bought what was supposed to be a 2003 WR450 cab, when I received it I found it is a 2005 YZ450 carb. There is a valve on the right side of the WR carb that is not on the YZ carb. It has a passage from the airbox side of the intake before the slide that leads to the valve. Anyone know what the valve is and any thoughts as to running without it?


It is the ACV (Automatic Coast Valve), used to reduce decel popping/backfiring.

Try the carb with the YZ jetting.

Thanks, Other than the popping is there any advantage/disadvantage you can think of to the YZ over the WR carb?

Edited by BIBMEN

I have a 2006 YZ carby on my 2004 WR450 - I was getting a lot of decel popping and was able to pretty much stop this by going up to a #45 pilot jet in place of the standard #42.

Combined with my FMF powerbomb exhaust, the carby seems to work well, providing a very 'linear' power delivery. Even the fuel economy has been good.

Thanks, according to the 2005 YZ manual it has a 45 in it so i might be good there. I will ride it some tomorrow and see how it acts. The main in the YZ is a 165 as opposed to the 150 in the wr. Aslo I do not engine brake much so maybe that will help as well. Thanks Again

I'm surprised that the US models ran a 150 main in the WR - we had a 160 as standard in Australia in the early models. I guess it would be something to do with different emission regulations.

My YZ carby has a 168 main in it, so your 165 should do fine, although it may depend how restrictive your exhaust is too.

Thanks for the thoughts

The main difference between the two carbs is the AVC. The needle jet emulsion tube is different (the WR one has holes on the sides, much like a pilot ) and I prefer the WR one as it is more responsive at lower throttle openings.


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