There are three basic types of tuning devices for tuning fuel-injected Harley-Davidson motorcycles. The first type is a “fueler”, which plugs in between the wiring harness and the fuel injectors. It has a few switches or controls, and adds or subtracts fuel in a few areas. The capabilities of this type of tuner are very limited, allowing adjustments to fuel only and only in a few areas. Advantages: Price Disadvantages: Poor results, and it adds extraneous hardware to the bike.”Fuelers” attempt to turn a very sophisticated computer program into a 3-circuit carburetor. Not Recommended. The second, and probably most common type, is a “piggyback” or auto-tuner device that plugs in between the wiring harness and the Electronic Control Module (ECM). It intercepts and modifies signals between the engine and the ECM. This type has more capabilities than the first, allowing adjustment to both fuel and ignition tuning. Advantages: Can adjust more parameters than the first type. Disadvantages: Adds extraneous hardware to the bike. “Piggy-backs” attempt to put the bike’s fueling parameters back into the original program, which may not be optimal for all performance levels. It is more of a correction device than a tuning device. Only tunes the areas where it is ridden at a certain RPM long enough for it to collect enough data for it to make adjustments. The third type, which is the best is a “Flash Tuner” does not add any extra modules. It loads a new “map” into the existing ECM. Advantages: Can adjust a lot more parameters than the other two types, and no extra hardware is added to the bike. “Flash Tuners” allow direct access to the program that actually runs the bike. Disadvantages: There really are no disadvantages to using a Powervision license type tuner. It is the most affordable and is guaranteed for the life of your bike.