Put an new aftermarket coil on, would run fine on tick over then drop out the rear two intermittently oily wet plugs.
Checked the resistance of the cheap coil and it was a bus ride away from standard.
Rebuilt both original coils with new silicone leads and NGK caps, popped a set of iridium plugs in for good measure. Ripped out the Keyster carb rebuild kits and refreshed all with genuine mikuni
Pilot's, mains and air jets to oe spec.
Then set the float height to about 2mm lower than the gasket on the bowls.
Second kick and she was away and has never been off 4 cylinders since
Bit fluffy at low revs but I think the carbs want an accurate balance job.
Hope this helps, never give up it will come good.
Dave UK
