A fuel injected two-stroke injector has about one third of the time available to deliver its load to a rather stationary mass of air. By pre-mixing the fuel needed with a small amount of air and spraying that rich mixture into the cylinder the time problem can be solved. However, this requires a separate system supplying pressurized air. Fuel will already be broken up into droplets by the time it's being sprayed and the rich mixture jet can be aimed at the spark plug, ensuring reliable ignition. The resulting flame front can then easily burn areas of leaner mixture.
Engines using an electronic injection-stratified charge system are available, but at a price.
Enter Piaggio's greatest stroke of genius since introducing the Vespa. The engine's bottom end is a regular clean burning two-stroke that pumps in clean air that will be transferred to the cylinder through the ports. Incoming air is throttled by one of the bores in a special double barreled carburetor. This half of the carb doesn't have any fuel jets, it only flows clean air. The real action happens in the cylinder head where a tiny crankshaft drives a small piston.