Originally Posted by fxrnutt

31 front do the trick?

Originally Posted by Foxster

The reason some tuners suggest removing the O2 sensors for bolt-on fuelers is because otherwise the bike tends to lose its tune in the closed-loop operation area (low throttle & cruising).

What happens is that the mechanic gets things nice on the dyno and then once you leave the shop and run the bike for a few miles the closed-loop system plus sensors reads the extra fuel the fueler is adding as a too-rich condition and drops the fuel back to more like stock. In fact, with HD ECUs, this also tends to have a knock-on effect on open loop AFRs too.

You don't get these problems if using a SEPST or TTS to do a proper job because you re-program the ECU and tell it what new AFRs to set for both closed and open-loop.

If you do fit a fueler and disable the sensors you should use eliminator plugs. This fools the ECU into thinking the sensors are still there and reading an ideal AFR and the ECU won't try to adjust the tune. Don't use the eliminators and the ECU thinks the sensors are faulty and the results are unpredictable. It might just throw a code and switch to open loop all the time or it might switch to limp-home mode with a very safe AFR and timing across the entire throttle range - not good.

The trouble with the relatively cheap solution of a fueler and no O2 sensors is that you have just disabled the most useful and adaptive part of the EFI. The engine will no longer be able to adjust as well for variations in air temperature, altitude and fuel. In other words, the tune might be spot-on for the exact conditions in the dyno shop but the tune will be immediately wrong as soon as you drive away and a lot wrong in the winter, up a mountain or if you put in a tank of US-winter-grade fuel.