All 2 strokes can be made to 4 stroke simply by richening the mixture enough. When they 4 stroke they literally "skip a beat" and the exhaust note deepens from the usual 2 stroking high pitched scream. The needle can be set so they're at a point where it can't make up its mind where it wants to run so then it'll switch from a clean 2 stroke to a 4 stroke then back again. This is the ideal setting to run in a new ABx type engine.

I have a graph of the pressures inside an engine while it's running in a 4 stroke and it's a very definite cycle of firing on one stroke, not firing the next stroke then firing again...over and over. The actual reason why they do this is still a little uncertain but it seems that when a very rich mixture ignites it burns fairly slowly and isn't complete when the exhaust port opens. This still burning mixture then mixes with the incoming fresh charge and contaminates it with exhaust residue. This contaminated mixture isn't able to be ignited by the glow plug so it misses a beat. When the exhaust port opens again most of this contaminated charge goes through leaving an almost completely uncontaminated fresh mixture ready to be fired on the next compression stroke.

Now here's a weird thing. This uncontaminated charge is actually fresher than what's normally delivered when running in a correct 2 stroke (even in 2 stroke mode there's still some mixing of old exhaust and fresh mixture) so it packs more punch when it's ignited. The end result is that when running in a 4 stroke the engine doesn't lose half its power as you might think but still puts out maybe 70% or so of the power it makes when leaned just barely into a 2 stroke. That's why there's not much rev change when it's switching between the two modes.