2003 WR450 2005 YZ450 carb

8 replies to this topic

Posted October 18, 2010 - 04:57 PM


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?

  • William1

Posted October 18, 2010 - 05:08 PM


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

Try the carb with the YZ jetting.


Posted October 18, 2010 - 05:37 PM


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

Edited by BIBMEN, October 18, 2010 - 06:14 PM.

  • pdunlop

Posted October 18, 2010 - 06:22 PM


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.


Posted October 18, 2010 - 06:29 PM


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

  • pdunlop

Posted October 18, 2010 - 09:36 PM


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.


Posted October 19, 2010 - 06:31 AM


Thanks for the thoughts

  • William1

Posted October 19, 2010 - 11:47 AM


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.


Posted October 19, 2010 - 07:52 PM




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