I dumped my WR in muddy water in the the spring of last season. After finishing that ride, I changed the oil several times but during the next dual sport, I started having engine problems. I ended up replacing the timing chain, cams, piston and rings. Im pretty sure everything is installed correctly as the bike starts and runs fine, but it developed a ping that my buddies hear while riding around me. Burns a little oil too, but I believe that is because of incorrect valve adjustment. I finished the season on that bike and parked it till now after the Oct. Dual sport. However, the problem that Im concerned with, is that after several oil changes and having just changed it today, the oil, after only running for a couple of minutes is already turning black, I only ran it long enough to check the level. Is it possible to flush out a motorcycle engine? Would that help? It seems to me that Im not getting all the old stuff out and its blending with the new. Is there something else mechanical that could be causing this?