Yep, that there is a LOT of carbon in the combustion chambers.
Here in the northeast US, we get a lot of our fuel oil from Veneuala in recent years. I have been told that while it is fine if it is used, if it sits for an extended period of time, the bottom of the tank turns into #6 fuel oil or 'sludge', which was never a problem with #2 fuel oil from the mid- east. So perhaps your gasoline has a higher percentage of solids in it than some gasoline from other places?
My suggestion would be to run some fuel injector cleaner through the bike every 5,000 miles or so and prevent that from happening again. And by the way, only use fuel injector cleaner on the last tank of fuel before an oil change as that stuff will turn the motor oil black and thin it WAY down in my experience. It is best not to leave a crankcase full of that stuff after using it but instead drain it by changing the oil.
Brian
All the valves