ignition cutout at speed

Spark to all four cylinders cuts out briefly at all speeds the tacho drops to zero all other electrics such as speedo and lights wok fine.

Check out the integrity of all block connectors.
The SV1000 has a known issue, with the same symptoms. The Green connector on the SV develips a high resistance and burns the pins. Hard wire bypass is the solution.
Look for pins that are damaged or corroded.
Very dangerous if you lose power mid corner.