This reprint of an old NGK brochure is the most comprehensive diagram of plug colors I’ve ever seen. Good stuff. It’s just a small chunk of Dan’s Online Motorcycle Repair Course: “Now, I’m not going to claim that this course will train you as well as a formal Motorcycle school. But then again it is FREE.” Thanks for the link, Nitro, (Who posted some photos from the Scooterworks ride on his moblog.)