Aftermarket instrument cluster
 

I have a Koso RX-1N speedo and tach on my F3 but I can't get the tachometer to work properly. If the calibration is set to 4 stroke and 4 pistons, it shows around 7k rpm at idle and it bounces around quite a bit, around +-1k rpm. I have read somewhere that the Koso needs a pulse signal but these bikes give out a different signal (varying DC?). Apparently there should be a converter for that, can anyone guide me in the right direction to get that thing working? It is quite annoying if the tach flashes red and shows redline when you are actually at around 4-5000 rpm.
I have tried every combination with the calibration and it doesn't really work better with any of them.

Also I think I should mention that my bike is an F3, but I'm pretty sure the engine has been swapped for a one from an F2 (based on the engine serial number).

You have 2 dual ignition coils, iirc you should set it to 1 cylinder mode and it should be sorted, might be 2 cyl mode if its wasted spark ignition type; thats why you are getting those super high revolution numbers. If the tachograph is very jumpy, do a knot on the wire to the tachograph to filter out high frequency signal noise, or wrap it a few laps round a salvaged magnet from any appliance you can find that has one.