The internal design and fuel delivery systems are all different, attempting to maximize the horsepower.
The 140 Sport has the tried-and-true YS pressurized system with a minimum of plumbing. It's also the lowest in terms of HP.
The 140L, which was discontinued about 3 years ago utilized a pressurized system which operated off the rear disc valve and incorporated a crankshaft sealing ring which allowed better internal pumping action. More power, but could be temperamental to operate.
The DZ is the first YS to use a true fuel pump rather than a pressurized system. It is the most powerful of the group.