The first step is to get the carburetor in a safe, workable state, which means the engine can run and that anything to do with high loads is set too rich. Then go throuugh the following steps:

1. Idle settings- not so much to get the best tickover but to let the engine pick up without hesitation from a closed throttle. In the beginning this is most important simply to get under way but as the other settings come together there are conditions at higher revs, where you've closed the throttle and then need to open it gradually, as if at the apex of a corner, when the engine needs to pick up smoothly. The pilot jet controls this region and it supplies fuel throughout the rest of the rev/throttle range so it's important to get this right early on, and with any luck it won't need to be changed again.

2. At the other end of the scale, the main jet and air jet control WOT (Wide Open Throttle) and this should be tested next, as long as the part-throttle settings let the engine run tolerably well. Start with WOT runs at the lowest revs the engine will accept and change the main jet to get this right of slightly rich. Then progress to higher speeds and use the air jet to control the mixture. If this isn't possible, or if you need very small air jets, repeat using a bigger main jet. Sometimes it just isn't possible, in one of their race kit manuals, Honda recommed a size zero air jet (ie the passage is blocked off completely).

3. Go through the part-load settings, at different (but steady) speeds and different throttle openings. Make a chart of where the engine goes rich or weak, which will suggest the best components to change for maximum effect. Correct any obvious deficiencies but don't try to get too precise.

4. From the data gathered so far, make a decision about the state of the intake and exhaust geometry. Does the engine need longer intake stacks or a bigger airbox? Is it worth altering the ignition or cam timing? Run some experiments to find out. Carburation can be used to compensate for poor exhaust and intake design, but only up to a point. If you have the ability to change intake or exhaust dimensions, now's the time to do it.

These tests beg the questions: "What is rich? What is lean? How is it measured?"

Chemically, a rich mixture will produce hydrocarbons and carbon monoxide in the exhaust. A weak mixture will leave oxygen in the exhaust. Sensors can detect these things. From an engineering point of view, the optimum mixture is the one that gives the greatest torque or the best fuel economy, depending on whether the engine is running on high load or light load. To determine this it's necessary to run the engine on a range of mixtures, measuring its torque and the fuel flow.

Some very high output engines use fuel for cooling: most of the fuel is burnt, the rest is merely evaporated, taking its latent heat with it and keeping critical parts like pistons at a safe working temperature. Chemically speaking, this is a rich mixture but it permits the engine to produce more power than the chemically correct mixture. For this reason you should keep increasing main jet or decreasing sir jet size until the motor is obviously over-rich at peak speed.

5. Repeat steps 1 to 3.

6. By now the engine should be running acceptably, in an overall sense. Go through the part-throttle settings, working from where the engine is best, towards the regions where it is worst. It helps to keep a clear record of the settings and the results, so that you can keep returning to the best settings. Where previous tests concentrated on maximum output, you are now looking for best pick-up, smoothest runing and best fuel efficiency, which arent so easy to measure.