This is the cut-off relay that cuts power to the ignition box when you switch the kill switch to 'stop', or if you engage a gear when the propstand is down. If it's fizzing and popping, it'll be interruptiong the power to the ignition box, hence the poor running. As the ignition box drives the rev counter, this will cause the erratic readings.
You could, as a test, connect the red/white wire to one of the red/black ones. This will bypass the relay and will supply power directly to the ignition box. Remember that this will also bypass the kill switch and the neutral switch/propstand circuit, so do at own risk.
This will be a fairly ordinary relay so could be replaced with any 12V automotive relay, ie one used for spotlights should work.
A wiring diagram for the Skorpion can be downloaded (in parts) from
http://autos.groups.yahoo.com/group/MZO ... lectrical/ and the cut-off relay can be found on the page marked 'Skorpion ignition & start'.
Hope this is of some help.
Incidentally, I'm organising a 'Skorpion Servicing Masterclass' at my house (near Paisley) soon. There's going to be 6 Skorpion owners so far, let me know (off group) if you want to attend.
All the best,
Norman
http://www.mzskorpion.net