Hi MT, Those engines are typical 2 stroke boat engines manufactured by a company called Dolphin in the 1950's and 60's ... They are not the same as the original dolphin type engine that uses a piston to charge the cylinder... http://www.dolphinengines.co.uk/history.php
Also I think most of the reason the Dolphin runs smooth is because it uses top / down uniflow scavenging... this causes the fuel / air near the spark plug to be in an ideal state for combustion. Ricardo also used a narrow passage to ensure the engine idled smoothly but IMO a narrow passage is also wasteful and not the best answer. I developed a different combustion chamber design which also allows for smooth running.
Most small carbureted 2 strokes use ether cross or loop scavenging which tends to not idle smooth... they also loose a portion of the unburned fuel out the exhaust which makes them not good from an emissions standpoint.
Modern low emission engines like the E tech and Orbital use a system that injects the fuel after the exhaust port is covered.