I've been having a slight problem over the past couple of days with lack of power, the bike would not quite touch 80mph.
It reminded me of when the diapragm went on teh right hand carb some time ago. In the workshop tonight I was checking the operation of the carbs and the engine cut out completly, with a very irratic spark.
I found the wires to the 4 pin plug on the ignition unit were faulty, 3 of the four wires were broken off due to corrosion.
To stop this happening to you, I suggest you take the plug out and make sure there is planty of dielectric (MS4 or something like it, Vasaline will work to) grease to stop the water getting in and causing corrosion.
Hope this stops others suffering the same problem.
Keith