The engine only has around 500 hrs and it just started running rough. Almost felt like it was missing and choking out. I know it has no carb so there's no choke to adjust. I pulled the plugs and one side has powdery black residue and the other was burning white!! It seems one side is real rich and the other real lean. I changed plugs and ran it some more and it seems to stay the same with the mentioned plug colors. I also changed the air filter just in case. It did run a little better after the plug change but I'm still getting that powdery black on one and not on the other. Any advice on what might be going on? Can a bad O2 sensor cause these symptoms? Thanks for your help.