jetting a 2008 wr450 with fmf full system?


  I am a proud owner of a beautiful 2008 Yamaha wr450 that i love to death. Coming into the 2014 summer riding season and i have struck a dilemma...


Ii have a FMF powercore4 and powerbomb exhaust system. 


I purchased a JD jet kid over winter along with the exhaust.


I live in Michigan, (north of Detroit area) and i cant seem to get my bike running back to normal, i have tryed changing jets provided in the kid to adapt to where i am, around 83 degree, and 700-1000 feet above sea level.


I do a lot of street riding because i am street legal but also travel the great state of Michigan to explore trails and just well anywhere...


But i am wondering exactly what needle jet to use (blue or red) with the C clip on which position, also which pilot jet and main jet, I am currently on the red needle jet (on 5th slot down from top) with the 165 main jet and the 48 pilot, and i feel i am close just not quite there...



You never stated what exactly the problem is???? What throttle position is the problem??

I suspect it is an issue on the street and not pulling well in the upper rev range?? I did a lot of Dual Sport riding last year and had that issue. If so, raise the needle and if that doesn't work, go to a 168 main jet. It needs more fuel in that throttle position.

If your problem is different let us know specifically what is happening.

Edited by crb357

The JD jetting kit address only the basics of jetting

You still need to upgrade and tune the accelerator pump system, and match you intake mods to you new exhaust mods

You also need to purchase an R&D remote fuel screw so you can learn to properly adjust your fuel screw.

Most  problems are not jetting, but apump and fuel screw / idle screw related


There are tons of threads covering 'accelerator pump upgrades' and 'uncorking and jetting'

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