On my '06 I did the white spacer mod, 1.25 turns out from stock on the idle mix screw, and went up to a 152.5 main jet all before the 600 mile break in. The stock set up is lean...period. So getting a bit more fuel into the system is fine. Plus it's really nothing the dealer will notice during the check up. After 600 I put on the sportster muffler and removed the air snorkle. I may have voided my warranty with the muffler change, but I don't expect to have any issues before my 12 months is up.
I always use high test gas (91-93), and notice better performance with it than with 87...I notice less backfiring with high test which makes sence to me because you end up burning more fuel per cycle than with 87...more fuel burnt = richer condition = less backfiring. I've never experienced increased plug fouling with high test gas...I'll need to look into that...as I understand the science (and maybe I don't
) carbon build up should be less with high test, that's why you put it in older (even low compression) engines that may have carbon build-up from years of low octane gas. The $$ for a couple gallons of 87 vs 92 is minimal. Carbon build-up comes from fuel that is unable to burn in the speed of the combustion cycle, high test burns slower within that combustion moment, therefore more complete combustion, therefore less build-up.
I, in no way, believe that anyone
should use high test, I just choose to for these reasons...
I'm always interested and willing to learn about the physics of the combustion moment, so if I have this wrong ???, please educationalize me