Hello Guys. Thanks for all the input. The fact that Mutha also had the same problem only after a service, put me onto the items I replaced. As I was loosing both cylinders, I took a look at the plugs (8EA as supplied by the bike shop according to their book). I could see from the colouring, that they were running very hot. When all else fails RTFM. (read the f... manual!) The manual specs a 9ea. So I go looking at the web and found the following:
Heat range

The operating temperature of a spark plug is the actual physical temperature at the tip of the spark plug within the running engine. This is determined by a number of factors, but primarily the actual temperature within the combustion chamber. There is no direct relationship between the actual operating temperature of the spark plug and spark voltage. However the level of torque currently being produced by the engine will strongly influence spark plug operating temperature because the maximum temperature and pressure occurs when the engine is operating near peak torque output (torque and RPM directly determine the power output). The temperature of the insulator responds to the thermal conditions it is exposed to in the combustion chamber but not vice versa. If the tip of the spark plug is too hot it can cause pre-ignition leading to detonation/knocking and damage may occur. If it is too cold, electrically conductive deposits may form on the insulator causing a loss of spark energy or the actual shorting-out of the spark current.

As I was experiencing similar problems, I went out this morning, and bought 9ea plugs.

Problem solved right away. Bike peaks out at 165 KMH again, and I have the surge of power back around the 7000 RPM range.

Kumuya if you are running the 8ea plugs, you must have set the timeing and or fuel mixture to compensate, or it is very cold there by you guys. We are running at about 30 deg celsius day temps here. Apparently all of the above affects the heat range of a plug.

The max torque is at abot 7200 RPM, so I change gears there about if I look for a bit of oomph! No use in running to the red line as the curve comes down quite a bit after 9000 RPM.

I hope this solution will help somebody in the future, as the bike shop books specified the wrong plug for my bike in our hotter climate.

Regards

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Pleco

If its stupid, but it works, it aint stupid.