I am finally ordering a FMF Performax II and a K+N filter today. My Question is, What size main jet should I run? I live in Buffalo NY, approx 1000' above sea level.
Thanks in advance.
-Justin

 

Since it is always safer to err on the side of rich, I'd buy the next two fatter main jets, install the fatter of the two and test ride at 3/4 to full throttle for a 1/2 mile or so to check for any cutting out or blibbering while on the gas. Then do a plug read by chopping the throttle immediately with no other riding at lower speeds. Check the color of the electrode & insulator for a lean or fat indication. What you want to see is a light tan or brown color for a good mix; a black or dark color shows a rich mix, & a gray or white color tells you you're lean. 1000' of elev. is basically on the edge of requiring a fatter main even when running a stock bike depending on the bike, temp, & riding habits.
If your plug read shows rich then just drop to the lower jet that you bought & re-test.

 

FMF will send a piece of paper that says what it should be. Mine said between 128 and 132, 132-135 if running an open air box, with a pilot of 42.

 

I live at around the same elevation as you and wound up running one over. I'm now running a 125 main. To be on the safe side as mentioned above buy at least 2 sizes over.