I have an 06 Rappy and tackled a valve check and adjustment myself. When I pulled the plug to do the valve adjustment it was BLACK. I have a PCIII and a K&N Air Filter (no lid). I double and triple checked the clearences of the valves prior to reassembling it. I put in a fresh plug and fired it up, after letting it warm up a few minutes i rev'd it pretty good a few times in neutral and it really back fired (fire out exhaust). Recommendations?