EC 300 2012 idle revs remain high
 

When started, it keeps rpms higher than normal for idle. Than I put it in gear, and release the clutch slowly with the brake on. Rpms drop to normal and stays low (I switch to neutral). Than I open the throttle for a sec and idle remains high again. The mixture screw is one turn out. I don't know what is inside the Keihin, I bought the bike a month ago and haven't had a chance to test it due to bad weather until now. Made few circles only on a field nearby and it pulls well, but whenever switched to neutral and rewed for a sec, revs stays high.

jetting
 

I suggest pulling the carb off, cleaning it and noting the jetting and float height
general location and elevation may help also. Take a peek at the reeds while there.

Check your throttle cable routing carefully. Wiggle the cable at full lock (both ways) and make sure it is free to move around. Does the throttle turn easily?If not, remove both ends and inspect for a broken cable strand.

Your jetting could be lean. As suggested find out what's in there. Another possibility is an air leak somewhere.

EC 300 2012 idle revs remain high
 

Have taken carb off: it is clean but bowl gasket is broken and I'm waiting for a replacement. Float level is ok, pilot #45, main #170, needle is NOZI (never heard) 3rd noch and throttle valve #6. Any suggestion for the altitude around 1000 feet?

Clean pilot jet

Double check and see if the rpms raise as you turn the bars lock to lock. Cable routing can cause this issues and so can handle bar risers.