New Exhaust - Carb Tuning

8 replies to this topic
  • jasnyder

Posted January 21, 2013 - 11:44 AM


I had asked earlier about slip on vs full system for my 09 YZ450F. I ended up picking up a [color="#22229c"]Yoshimura[/color][color="#282828"] RS-2 full system. Do you any of you have any suggestions as far as jetting or carb adjustments. I have heard of a couple of ideas, matching the '06 specs or going with a JD Jet kit. Not sure what all would need to be changed if trying to match the '06 specs. [/color]

[color="#282828"]Has anyone had any experience with the JD Kits? [/color]

[color="#282828"]We ride at 1500-6000ft, 40-90 degrees depening on the time of year an if we are riding the desert or the mountains. (Eastern WA)[/color]

[color="#282828"]Have not had a lot of experience with carb tuning, especially when changing the exhaust, any suggestions on what needs to change and what to change it to would be appreciated. [/color]

  • highmarker

Posted January 21, 2013 - 01:18 PM


unless your way off now it shouldn't make a that big of difference in jetting, I'd ride it and let the bike tell you if needs adjusting. Not really needed but easily adjustable fuel screw is nice to have for when the altitude gets high and the bike doesn't want to idle or decell popping coming back down,

  • grayracer513

Posted January 21, 2013 - 07:19 PM


'08's and '09's are very close to identical, and this one ran as well as any I've seen:


As far as altitude and temperature compensation goes, rule of thumb is roughly 1% leaner jet number for each 1000 foot gain in altitude, and 1% leaner for each 10 ℉ rise in temperature. As you can see, then, it would take a 3000 foot climb or a 30 increase in temperature to move from a 165 to a 160, or from a 45 pilot to a 43. The fact is, however that four-strokes in general just aren't all that fussy about it.

I ride from 80 feet below sea level to around 4000 above without changing anything except a bit of trimming at the pilot screw. I do change jetting seasonally between a summer time 165 and a winter time 168, but the bike never fusses in temperatures that can range between 40 and 90, or 60 to over 100. Todd's jetting should be a great place to start. The needle change improves throttle response on sudden openings.

  • jasnyder

Posted January 21, 2013 - 08:32 PM


Thanks Gray...

One other question for you, when I got the pipe I was also given a Boysen Quick Shot (1st generation). In your opinion do you think it would be beneficial to put it on when I change the jetting to match Todd's setting. Also, do you know what clip position he set his needle at?

Edited by jasnyder, January 21, 2013 - 08:41 PM.

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  • highmarker

Posted January 21, 2013 - 08:47 PM


Riding WA mt's is a summertime thing and you WILL boil a 450 on those steep grinds and climbs and slow cliffhanger trails. Better not to try to rejet for the alt and let it be a hair rich.

  • grayracer513

Posted January 21, 2013 - 09:58 PM


Also, do you know what clip position he set his needle at?

I believe it was 3, like stock. Don't know for a fact, though.

  • jasnyder

Posted January 22, 2013 - 07:59 AM


Any suggestions/opinions on the Boysen Quick Shot?

  • grayracer513

Posted January 22, 2013 - 09:32 AM


It has no advantage to offer other than it does have a slightly better check valve system in it than the OEM cover, but the OEM checks seldom cause any problems. They were good on some of the older bikes, not so much anymore. I'd sell it.

  • jasnyder

Posted January 22, 2013 - 09:41 AM


Thanks Guys...

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