Hi Kamm Matt,
For my bike it turned out to be a combination if 2 things. Firstly the 2004 RSV factory came from Aprillia with a poor fuel map, map 1 and got recalled to have the map changed to fuel map 2, this can be done by performance Aprillia from Tamworth or your nearest Aprillia dealer. Secondly with my bike the sprag clutch was on the way out, in that it was beginning to break up, this was causing small metallic debris to collect on the crank sensor which is a magnetic sensor, which in turn threw the ecu fuelling out due to incorrect readings from the crank sensor. Hope this helps mate.