Just had my 600 out today after the winter lay off.
So,got it up and running,warmed up and hit the road.
So,I did have the carbs off this bike last year, cleaned,balanced and bike was fine.
So,I set off and 7-8 k,a bad flat spot where it feels the fuel is cut off then back on and the bike continues to the red line. More noticeable from 3rd gear up.
Checked pump,it's going,new fuel filter too.
Only thing I can think is maybe new plugs will cure it because I never changed plugs in my ownership so god knows when the plugs were last changed if ever!