Originally Posted by Ulyses
My pleasure man! Thanks again for all of the help. The bike definitely lugs at high altitude though, even with a clean filter. Surprisingly, a lot of my riding has been above 5,000 feet. I may be getting up above 13,000 feet soon; would you recommend re-jetting (I brought extra jets) or just adjusting the mixture screw? By the way, where is the mixture screw? Haha. I'm such a damn noob when it comes to mechanical stuff.
I did! I was a little worried the first time I did it though; it looked like it was permanently inside the foam. Thanks for the reminder.
Trust me, a lot of people have been tricked by that Uni air filter, especially because of the foam strap located on the bottom of the filter, and because the "button" fits so tightly on the post.
One doesn't need to adjust the pilot mixture screw for different altitudes. If your bike has been running well, your pilot mixture screw (PMS) is probably set correctly.
I am using a size 55 pilot jet, and a size 155 main jet in my XR650L's carburetor. My bike runs well from 4,600 to 9,200 feet above sea level. Another XR650L owner has reported his bike runs well from sea level to 14,000 feet above sea level using the same carburetor jets. However, a lot depends on whether you have performed Dave's Mods, removed the air box snorkel, et cetera. Neverthless, the constant velocity (CV) carburetor on the XR650L does a pretty good job compensating for altitude.
What jets are currently installed in your carburetor? You might want to go a size lower, at least on the main jet, when you begin riding at 13,000 feet above sea level. You can change the carburetor jets without removing the carburetor.
I suggest you see how well the bike runs at high altitudes before you decide to change carburetor jets. If you need any help, don't hesitate to ask. We can tell you how to change the jets easily.