So I recently cleaned my carb and everything seemed to be running well. I have a jardine exhaust on my 2005 250 and one side, or pipe rather has turned quite blue. I also get some backfiring when I left off the gas and I come down into the lower end of my rpm's. SO I'm wondering if I'm running a bit lean or a bit rich, and then what would be the easiest route to solve this. I've attached a picture of the exhaust that's blueing and the spark plug from that side. The tip seems to be a neutral color but there's a ring around of black.