My bike has a terrible flat spot from ~2100 to ~2500rpm... it feels like you're about four gears from the wrong place. If you're in a low numbered gear (like 1st) it is a little flat and then lurches when it hits 2500 and rides 'normally' like you'd expect. If it's in a higher gear (eg. very low-throttle very low-rpm cruising like 5th at 60km/h on a flat road) then it's really flat and when it reaches the spot that it would 'clear out' in a lower gear it sometimes clears out but often just misfires - it almost sounds like it's forward-firing.
Rides fine everywhere else, on the dyno it's fine & the curve & afrs are much like I'd expect based on my last ZX12R even though this one is a little tired / lower numbers.
I've tried it with & without the power commander so it's not a mapping issue. Always run on premium.
The bike itself is a B1 ZX12R, I don't know much of the history but it's not exactly immaculate. It has a full system on it, otherwise it appears fairly standard. Not sure if there are any other unseen mods like air filter, ignition advancer, etc.
Any thoughts/opinions appreciated. Need to fix it for no dollars, or live with it