ORIGINAL: Pat Roy
You don't think that most 100cc twins use the same cylinders they use on their 50cc engines? A 3w-56 is a pair of 23i cylinders. A Brison 105 is a pair of 3.2 cylinders. It's a fact of life everywhere.
I'd never really noticed it before (the cover plate on the intake ports) on other engines, until I noticed them on the in-line ZDZ twin. It makes perfect sense, why have to make separate castings for the same displacement cylinders. I had thought to give the SV-50 a try as my first twin; price is reasonable, most others are too rich for my blood (and wallet).
I guess even GM, Mopar and Ford get into the act, sawing off either one bank of a V-8 to make a slant 4 or the front two cylinders to make a V-6.