[Scott Paske]

Ok need a little help from you experts. I just bought a 2005 CRF 450x in good shape but all bone stock. I opened up the air box by taking top off completely. I also took the baffle out of the stock muffler. My question is would a 165 main jet be good for that set up. Also should it start when could any better. I have looked at the jetting section but still a little confused. Thanks so much for any help. I love this bike.....

[JimDirt]

Use this guide as a baseline


Sea level....165
2000 ft......162
4000 ft......160
6000 ft......158
8000 ft......155

I ride between 2000 to 8000 and run a #162/45 , Needle on 4 clip position from top , #65 leak jet , 1 1/2 turns out on fuel screw , i have airbox cut,R muffler,HotCams Stage 1...06 X

So if you are around my elevation , then what i have should be close enough for your bike , if different elevation , keep everything as mine is (basically) and adjust the main jet size according to your elevation.....or just do what everyone else around here does (excluding me) and get a JD Jet Kit

[Scott Paske]

Thank you for your help!!!

[hazard88]

If you opened things up a bit you might want to move to the 45 pilot as well. I think stock was a 42.

I would suggest going through the Jetting Database here and look for those with similar elevations and mods.

I have the 06 X as well. I also removed the backfire screen and went with just a flame resistent air filter.
I ride at Sea Level to 4000 and I have NCVS Needle 4th clip, 45 Pilot, 165 Main, 50 Leak and 1 3/4 turns out on the screw. There are other carb mods you can do on that bike around the AP circuit to remove some bog but you can find that info here too when searching.

Good luck