I am based in the southern parts of Sweden.

The most recent update follows.
A few weeks ago took a second look at the bowls and you were right, the "plugs" are jets. Turns out that the ultrasonic cleaner cleaned everything except the jets... I ended up pushing a 0.2mm drill bit through the dirt! I decided to take a look at the floats since i have been convinced that my problem was caused by overflowing carbs so i followed the haynes manual thoroughly. The measured fuel level was, according to manuals and instructions on other sites, too low made no sense to me since i was convinced it was the other way around. I set the floats according to the manuals without any success. The next thing i did was to cut the fuel supply, let the bike idle and rocking it back and forth to see if there was a point were the problem disappeared. The bike died a few times but after about 1-2 minutes i could rock the bike violently without it dying. So i removed the carbs once again, set the floats slightly lower than specs, and in a way so that the floats weren't parallel the fuel level upon closing of the needle valve and mounted the carbs again. I fired the bike up not expecting any difference tried a medium brake and nothing, it didn't die on me. so i started rocking the bike and it jest kept on purring.
In short terms, i have finally solved my problem which did only take a few years to solve....   I haven't had time to check the actual fuel level again after i got it working but will do so when i have the opportunity. Could the problem have been caused by the floats closing at somewhat correct level but not pushing the needle enough so that upon braking the the fuel level shifted causing the floats to temporarily let of the pressure on the needle causing excess fuel to flow into the bowl?

Thank you everyone for your comments and ideas. To anyone who experiences the same or similar problem/s as i did, my recommendation is to cut the fuel supply and let the bike idle to see if the fuel level in the bowls is the cause.