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Jetting 2008 crf450r?

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Wondering where to start? All stock bike. I ride at 3500 ft and up, but want it dialed in at 4000-4200 ft. Temps are 60-80. I have adjustable fuel screw.

Thanks.

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It should run just fine stock from 0 to 8000 ft.

The stock jetting is very good. Third postion from top on the needle.

Fuel screw adjustment on a HOT engine at each ride is key. You lower the idle as low as it will go, then raise it with the fuel screw. 

HOWEVER, if the bike has any real hours on it, you will want to replace the slide plate seal, and the needle jet (emulsion tube) for the cripsest repsonse.

Make sure you are using a BRASS fuel screw, as the allow ones are tapered, which is no good.

 

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I haven't ridden Honda's latest 450,  but none of the ones that I rode since 2008 were as pleasing to me as the 08 was.  If you are unhappy with,  or want to see what you can gain from yours it should be easy with a few "try it and ride it sessions".   My crf250 is jetted for sea level,  and with a higher than stock compression ratio doesn't seem to mind changes up to about 3000-3500,  but our air for the most part is drier up there.   by 5000 it is noticeable.   Honda probably has some jetting suggestions in their shop manuals if you want a starting point.  I ride with guys who have orange,  blue,  and red 450's,  they seem to notice the changes about a thousand feet further up than me and it starts for most with an idle that is slower and harder restart,   so your fuel screw is a good place.

If you are happy with it from 0-8000K ,  you probably don't want to change a thing.  :rolleyes:

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I dug up some of my old notes for you.  I dont have my 08 anymore, but it was the best 4 stroke at the time.  I loved it.

My settings on my 08 were at 5000' up to about 8000'

 158 or 160 main

42 pilot and the needle clip one position leaner than stock, (can't remember what position that is.)

Get an R&D external fuel screw.  Then you can adjust it with your fingers easily depending on temperature and conditions.  Makes a big difference

runs awesome, starts easily, even when hot, and even in gear. At lower elevations a lot of guys run a 45 pilot and that cures their starting issues.

I had over 120 hours on it with that jetting.  Never a problem from slow singletrack in Moab to WOT desert 

 

The 158 or 160 main is a big jump from what comes stock but that bikes stock main jet was rich even at sea level.  This was confirmed to me buy Eddie Sisneros, the jetting expert here on thumpertalk.

Edited by rdalley
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Did you try any of the suggested jetting and how did it work out?

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