Like all engines, the primary job of your bike's motor is to turn the energy contained in its fuel into kinetic energy, or motion. It does that by burning the fuel inside the combustion chamber (hence "internal combustion engine").
Gasoline requires oxygen to burn, so one of the most crucial tasks of an engine designer is to get both the fuel and oxygen inside the engine. From then on, you can start worrying about compression, ignition, getting rid of the waste gasses and a whole heap of other worries. But without fuel and oxygen inside, your engine won't do very much at all.
Oxygen is easy-there's plenty of it in the air we breathe (typically, air is 21 percent oxygen, 80 percent nitrogen and nine percent "other"). So the simple act of moving your engine's piston down to the bottom of the cylinder while opening the inlet valve will fill the cylinder with enough oxygen to burn a useful amount of fuel.
Getting the fuel into the cylinder is slightly trickier. In the old days, bikes used carburetors, which used the engine's inlet vacuum to suck the gasoline through small jets. As you opened the throttle to let more air in, the carburetor opened more along with larger jets, letting more fuel spray into the inlet airflow.
Nowadays, bikes use fuel injection to get the fuel into the engine. The main reason for the change is emissions legislation-fuel injection makes it easier to reduce unburnt hydrocarbons and other nasties in the exhaust gasses through better fuel atomization. But, there's a much more positive side to the change for us, which is easier fueling adjustment. Carburetors don't really allow easy adjustability-if you've ever stripped a bank of carbs off an inline four engine from the 1990s, you'll know what a pisser it can be.
Four carbs mean it'll take...
Four carbs mean it'll take time and frustration to get the fueling right. There aren't any plug in computers like an FI box.
With a modern fuel injection setup, and the help of some pretty cheap electronic gizmos, you can alter the mixture at any point in the rev range to suit an altered exhaust system, race cams, different inlet, or even a bolt-on turbocharger kit. And it's as easy as plugging in a laptop and typing in some numbers.
The most popular fuel injection tuning aid, by far, is Dynojet's Power Commander. Dynojet started selling replacement jet kits for carbs, and quickly saw the way the world was going in the late 1990s-switching to fuel injection tuning. Dynojet's not the only firm offering a fuel injection tuning box. Bazzaz Performance, Yoshimura and Two Brothers also offer their Z-Fi, EMS and Juice Box units, which work in a similar way to the Power Commander. We've had good results with all of these, but we'll use the Power Commander as an example, simply because there are so many out there.
 Fuel management boxes come...  Fuel management boxes come in different shapes and sizes, but they all make dyno tuning quick and easy. |  | |
At its most basic level, a Power Commander intercepts the signals between your bike's standard ECU and the injectors and alters these signals to make the injector squirt more, or less, fuel into the engine at any point in the rev range.
How does it do this? Inside the PC is a small piece of memory that contains a "map" of injector adjustment values. Imagine it like a grid-along the top is the amount of throttle opening, and down the side is the engine RPM. At each point on the grid, the PC stores an adjustment value, which it then uses to alter the injector opening time at that point in the engine's cycle.
So, say your motor runs a bit rough at 4,000 rpm on 50 percent throttle after fitting a race pipe. Using the PC interface software, you can dial in a little less fuel at that point. So when the PC intercepts the injector opening signal, it reduces the amount of time the injector is opened, and cuts the fuel supplied by the amount you specified. As well as the connections to the fuel injectors, the Power Commander also connects to your bike's battery, and (usually) its throttle position sensor.
How To Fit A Power Commander?
Fitting a Power Commander is actually pretty straightforward-so if you have some basic wrenching skills, you can give it a try. The unit normally mounts in your tail unit or under the seat, and plugs into your battery negative supply, the injectors, and also the throttle position sensor. The battery connection is simple, but the others can be finicky. You'll have to raise or remove the fuel tank to gain access to the injector connectors. Remove the stock connectors, and plug them into the appropriate PC connectors. Then plug the PC's injector connectors into each injector socket. Finally, the throttle position sensor may be a plug, or a small tap connector. Put the tank back on, and you're ready to roll.