From introduction: "Tuning for performance will get you the most of your motorcycle. Because it is fundamental, it applies to any kind of bike-street or dirt, stock or modified. The idea of tuning to air denesity is not new to professionals. Record-keeping is also not new. It is probably the most effective "tuner's trick" and it reduces labors while improving results. Blank record forms at the back of this book will get you started keeping records, if you are not doing it already. Theory is linked closely with practice. Tuning adjustments are described in terms of what they do and why. Then they are described from the practical standpoint of how you adjust them and where you find them. When the chips are down, we will be guided by what we see happening. An important element of rational tuning is making tests to find out what the result was. Testing gives you the only valid indication of what a tuning adjustment did and what you should do next. When it gets down to the nitty-gritty of making your bike run well at a particular place and time, the owner's manual may not be very helpful. The same is true of hop-up instructions. They will usually give initial settings and say something like, "Tune for best performance." Another blank wall. The main purpose of this book is to cut a door in that blank wall and invite you through it.