This will make the bike run quite a bit richer. This ECU was provided with the full Termi exhaust which removed the cat. Overall, the bike breaths much better with the full termi exhaust; however, this ECU still makes it run overly rich. If you see any Multi with the full Termi system, you will see the exhaust is pretty sooty. It will be even more so if you put the ECU in with no changes to the intake/exhaust. It will probably feel a bit smoother at lower RPM, but you are likely to foul plugs.