Hi Bob
I haven't seen the article yet, but there was a feature recently in Practical Classics with a dismantled engine from a Trojan tourer that i thought at least partially explained it. Because the inlet and exhaust ports usually share the same cylinder on a two-stroke, some fuel passes straight from the inlet and out through exhaust without being used, so giving poor fuel consumption. On the Trojan, you have two separate cylinders joined only at the top, with inlet one side and exhaust on the other. You also have one piston moving slightly ahead of the other (on a shared, slightly flexible con-rod). This allows the exhaust port to be covered for longer during induction. I'm guessing it's advantages were maximised on such a simple low revving and fairly crude (cheap) engine where the number of components would be far less than an equivalent four stroke.