Hi Converse. I guess by now you have got your answers, but in case...
The twin has a crankshaft with two big ends, 180 degrees apart. Hence both pistons go through the same strokes.
So you have two pistons compressing the fuel/air/oil mix in the crankcase, at the same time.
Both are on the compression stroke at the same time, and fire at the same time.
That means that the firing strokes oppose each other. The engine is smoother than a single cylinder of the same size for this reason.
If I remember correctly, and I will accept a counter-argument, that the two spark plugs are wired in series, similar to a wasted spark ignition, as used for example on the Commodore "Ecotec" engine.
This should almost guarantee both plugs fire, or if there's an open circuit, no plug will fire. Trouble is, the rear cylinder (on the twin) runs colder than the front cylinder so that plug fouls up first. That creates a short circuited plug which means the front cylinder still runs. Many of these twins ran on only one cylinder for that reason.
Victa did several (!!) mods during their life to alleviate the many problems they had, including running a "hotter" plug in the rear cylinder. I wonder how many back-yard mechanics didn't know this and while attempting to fix a "running on one cylinder" fault, swapped plugs...
I have used my twin on several occasions. It is very smooth! It cuts my lawn heaps better than my old Jetfast (but I think a pair of scissors could do that too!)
I can mow my lawns MUCH quicker with the twin.
I intend to put mine up for sale soon, I have one complete and three other engines plus various other parts. That will be after Christmas when i can get some clear air.
Hope that all helped.
