spark plug NGK B9ES instead of B8ES

[gert du prez]

Ok,
so that would also mean that the difference I think I experienced in the engine between the B8ES and the B9ES are purely 'in my head' and not in the cylinders (if that expression exists in English) ?

[GSexpress]

What Bakes didn't include is that ambient conditions also effect combustion temps. cooler or hotter climates and cooler or hotter burning fuels change the conditions. That's why the manufacturer has more than 1 heat range listed for use. In our case those recomendation were before the common use of alcohol mixed and unleaded fuels. The fuels we have now don't burn as hot. and therefore a colder plug may be too cold, particularly in a colder climate as the cooler air also causes cooler combustion temps.

If it starts to get a little hard to start when cold and has a hesitation or stumble when you whack the throttle open, then the 9's are too cold for your riding conditions. It may take some miles for that to show up as it builds up some fouling deposits.