I haven't seen performance reports comparing the Lawn Boy engine with the Japanese ones, but I've seen plenty of rave reviews of the Japanese ones, and none of the Lawn Boy. If you check the Youtube videos you'll notice it runs better than a Victa, but just about anything short of an old British engine does. Lawn Boy used automatic ignition advance instead of fixed timing, and they had a reed valve which improves smoothness at low speed and idle. Aside from that it seems to be just an engine. The D series looked rather elegant, partly because its carburetor, air filter and reed valve assembly mount on the opposite side of the crankcase from the cylinder, so it looks like an opposed twin. The ones with the carburetor on the side of the crankcase instead of the bottom, just look like engines to me.
