| The eprom is in the silver aluminium box under the pillion area of the seat. There's a black rubber bung, usually covered by a sticker or tape. The eprom is directly below this bung.
The eprom can have whatever fuelling/ignition maps stored on it. These are "burnt" on there using a PC and the relevant software.
IMO, a bespoke eprom would be better than a PC.
Cost wise, you'd need to talk with people like JHP or AJRacing. I don't have the equipment or specific knowledge to get into this kind of work.
A PC is £300 or so, and even then you're stuck with "off the shelf" maps. If you wanted the best possible results you'd need some dyno time to dial it in correctly.
£300 would buy you a good few hours on a dyno and JHP only charge £30 or so for the actual eprom. | 
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