jetting

[Cat Bandit]

So i touched on this before, but the page is gone now, but i have an 09yz450 with a new mountain horse kit, and I'm trying to figure out how much to jet my bike. I'm gonna start with one size up on the pilot, and maybe raise the needle a click, but do i need to richen the main? I'm gonna be riding in the same area a during the summer, and it seems ok then...thanks for input, and hope for snow!

 

[mtn-doo]

I don't have your YZ, but you're on the right track. If the altitude is the same as your summer riding, you will want to richen things up a tad ONLY if you were spot on in the summer. The colder temps will push your density altitude down about 1500ft. Stock bikes always run rich, I would say that you can leave it alone and be real close. Dealing with snow and limited air, they tend run rich anyway.

 

[Robster]

I don't have your YZ, but you're on the right track. If the altitude is the same as your summer riding, you will want to richen things up a tad ONLY if you were spot on in the summer. The colder temps will push your density altitude down about 1500ft. Stock bikes always run rich, I would say that you can leave it alone and be real close. Dealing with snow and limited air, they tend run rich anyway.

I have changed the main on my wr450 -06 to one size richer during winter, since both the yz and the wr header get really red after less than a minute just idling. In my book that is due to that they are pretty leaned out stock. It will also help when cold starting if you went up a size on pilot jet too.

 

[Cat Bandit]

I have changed the main on my wr450 -06 to one size richer during winter, since both the yz and the wr header get really red after less than a minute just idling. In my book that is due to that they are pretty leaned out stock. It will also help when cold starting if you went up a size on pilot jet too.

so I stepped the pilot up one, and will try it tomorrow. I ran stock today, and it was popping, and farting, so I figured it was a bit on the lean side. I also rolled the throttle really slow, and by about a third, to half throttle the popping went away. So Im starting with a step on the pilot. as far as the header glowing, the timing is pretty far advanced, which makes the lean worse, plus if you've never had the header off, its paper thin, so a lighter would probably make it glow!