Yes it matters what elevation your at. My Mods may be different than yours. But, when I was piped jetted and air filter I ran 150/155 from 0-6000' Everything worked fine for me like that. That was a happy medium for all my riding conditions. A tad rich at higher elevations but damn good at the lower. When I get my 686 together and running Ill be starting out with 165/170 and see how it goes from there.