I have been having multiple problems with my cbr. when I come to a stop it will idle at 1000rpms and will slowly die. the throttle lags a bit and responds slow. when riding it will not go past 7000rpms. I have just recently replaced the spark plugs 2 of them were burnt pretty badly, that did help with the response and going about 7000rpms but now it is back to the same problem. I also get 40mpg.

I am pretty new to bikes don't have a lot of mechanical knowledge on bikes anything helps.