On the EFI bike the problem is going to be with the O2 sensors, they are located on the exhaust headers.
A free flowing pipe will have the senors sending feedback to the ecu. The ecu then try's to correct mixtures (within the limits that are mapped in to it). Which means, (as stated) remapping.
The solution I used was TUNEBOY programme which bypassed the O2 sensors.
Steve
