2004 ZX10R crank speed sensor

[Calumh96]

Im looking at checking out a fairly cheap ZX10R over the next few days.

The owner says he recently have a crank speed sensor fitted and it hasn't been set up with the power commander.
He says below 4k revs the bike misfires but past that runs as it should up to redline.
He says it wasn't like this before he fitted the sensor. Could be plugs coil or over fuelling.

Thoughts? what am i really looking at here?
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Current - K1 GSXR 600
Previous - K5 SV 650, ZR750, Lexmoto Adrenaline, HondaCBR125R, Lexmoto Arizona, Senke x6, Yamaha YZF125R, AJS DD125e, Hyosung Gv125, Jinlun JL125