Two layers with respectively 10 and 11 samples, themselves subdivided into two categories: V4 2-stroke and I3 4-stroke samples. This disposition allows to play with samples' volume -- which permits to match more accurately realistic multi-cylinder 2-strokes. The downside of this technique would be that it isn't performance efficient (21 samples managed at once).
Concerning this video, the output sound was meant to replicate 3 cylinder 2-strokes' with a certain degree of accuracy, but still needs tweaks and probably new samples.