I agree with draining the fuel out of the system. I would wait on the plug change out just yet unless it was stock plugs and start from there.

 

I was just about to post about plugs, i was reading my manual about knocking noises and the main to reasons it gives is bad fuel and fouled plug, i did notice when i took the engine apart that one plug looked a lil bigger than the rest. Anyways wish me luck, im on my way to get some plugs and a siphon.

 

sea foam lowering the octance was my first thaught as well. once you get a fresh tank of gas,your gonna have to run it for a bit to finish getting all the seafoam out of the floatbowls. I can run my bike for a while without the tank on it.