I took the wr426 out yesterday and the thing was running like hell. i had dropped the main one size because i was heading to the high country but did not go. I took the bike out for a ride,not thinking one size would make a diff.. It was popping and backfiring like crazy.I put the other main jet in and it still was back firing. Ichecked the plug and it was a sooooty black color.I am not sure what would cause this?