I have a 2002 Z 570 that I have been loving for years now. It's got about 5,000 miles on it, I am not too sure... the speedo went out 2 years ago. It had never had any major problems until this year. Other then body and undercarriage issues, this year the engine burnt up, but it was just the left piston. So i replaced both pistons and all the gaskets and the cylinder head and cleaned the air box and carbs and the machine rode like a champ for about 4 days while I was breaking in the engine again and on day 5 I started to notice a bogged down noise. Pulled the plugs and the left plug was white. So I took the cylinder head off and the left side on the head was black while the right was clean. And the left piston was black while the right was clean. I was able to wipe away all the black built up (luckly!) and replaced the plugs with new ones and went for a 10 minute ride came back and pulled the plugs and the same thing... the left side was white, while the right was ok. I've rebuilt this engine, cleaned the carbs, cleaned the airbox. What could be the problem. I really don't want to burn up another engine.... Please Help! I Love my Z and was hoping to race it this year just for the fun of it!