I was riding at the Badlands in Attica, IN this weekend. I have an 05 yz450 that I recently put a big gun ehxaust and header on without rejetting the carb. As soon as I put the pipe on I could tell a difference in the power and the bike seemed to run great so I rode without rejetting for 5-6 rides. This last weekend I was at at the Badlands and bike seemed to be riding fine but at one point I cut the engine to wait on a friend and it wouldnt start again. I had to push my bike outta that bitch. I removed the spark plug and it was straight black. I popped a new plug in there and she started right up and rode great for the rest of the weekend. Any ideas why the bike fouled the plug and what does a black plug mean? too rich or lean?