Bike idle issue

What's going on guys? I'm having a little issue with my bike. So awhile back when I would take off in first gear, my bike would sound almost like a v-twin and would barely have power until I hit about 6000 RPM's, then the power would go to normal. It would do that every time I took off in first so my first thought was I needed to change the spark plugs. After I changed the plugs, it got alot better and it seemed like the problem was fixed. Well the other day I was riding, and after about 20 minutes out, I was at a light with my bike in neutral. It was idling around 1500 RPMs and every couple of seconds it would drop to 1000 RPMs and make a hum noise and then shoot back up to 1500 RPMs. It would lose a little power at takeoff but not nearly as bad as how it was before I changed my plugs. My only thought is maybe it is a fuel issue? I always put premium, never cheap gas so I'm really confused as to what this may be. I was just wondering if anybody knows what the hell is going on or if it has happened to any of you guys?