Octane rating shows the fuel's resistance to pre-detonation. Period. If the bike does not knock and ping on 87, then 89 is a total waste of money, and the mixture can not be leaned out or richened by changing the octane rating of the gas.
Most bikes come from the factory on the edge of too lean, to help meet EPA emissions standards.
Pulling the baffles screwed up the mixture. An engine is basically an air pump- 14.7 parts clean air and 1 part gas in, heat and dirty air out. When you modify the exhaust you change the amount of air the motor can pump. Unless you remap the FI unit or change to an aftermarket one from Cobra or Power Commander, you have not adjusted the amount of fuel available to mix with the air. On some bikes exhaust mods make the motor lean, on others it makes it rich, depending on the intake system, the fuel processor, emissions control equipment, and other factors. And sometimes the exhaust mods will cause the bike to run lean at idle or steady throttle and rich on hard acceleration, or rich at idle and lean on acceleration. I can put the exact same pipes on two identical bikes, yet end up with different jetting to make then run right. That's why remapping a FI unit or rejetting a carb correctly is so hard, more of an art form than a science.
As an example, when I changed exhaust on my Harley the idle/ closed throttle circuit was WAY too lean, steady throttle was fine, and hard acceleration/ high speed was just a touch lean.
Backfiring is a sign the mixture is off. It is NOT always a sign your mixture is rich. A bike that is running lean will backfire because the mixture is so lean it does not ignite. The unburned mixture gets into the exhaust, where it does ignite, causing a backfire. A bike that is too rich will also backfire, also because of the unburned fuel in the exhaust, or sometimes because the extra fuel momentarily fouls the plug, causing it to not fire, dumping the unburned fuel into the exhaust.
If you backfire on hard acceleration you are probably too rich on the main circuit of the carb or power band of the FI map, if get poor performance under hard acceleration you are probably too lean. If you backfire on deceleration, at idle, or at steady, part throttle, then the idle circuit of the carb or idle band of the FI map is too lean. If you backfire while holding a steady speed, the middle circuit or middle part of the FI map could be either lean OR rich.
Have a headache yet? LOL!
So the short version is don’t assume that the bike is running rich because it is backfiring. If could be lean.