Unlike a 4 cycle, the fuel metering is all controlled by the injector and a throttle control lever on the injector actuated by the "rack," just a long bar that controls all injectors simultaneously. "Adjusting the rack" is how you tune a DD fuel system. If the rack is not adjusted properly, the injectors will get either too much or too little fuel and the owner won’t have a happy face. Between the two engine types, the injectors are the main show on DD engines; the fuel pump is the big deal on 4 cycle engines -- i.e. the gizmo that eats the most greenbacks. On a DD individual injectors can go bad without jeopardizing the whole system. With a 4 cycle engine, when the fuel injection pump goes, its lights out. Two advantages of the DD fuel system is that it is considerably less sensitive to fouled fuel, plus the injectors are self-priming so that you don’t suffer the priming problems often encountered with 4 cycle engines. While the injection pump system is more reliable and requires less frequent service, the DD injectors are more efficient.
High Performance Parts for Piaggio Engine Morini Engine and the Mineralli Engine used in Aprilia Scooters. There is another engine called Prue Jet maybe from Paiggio that I do not know enough about. This is a picture of engine types so you know which engine you have.
V-8's and V-6's engine types exist today in many American cars and trucks. The cylinders are located on oppsite sides of the crank shaft and are elevated up a varying amount of degrees depending on the manufacturer. The V-type engine is known for using a pushrod valve system. Usually V-6, V-8, V-10, and V-12.