A Whizzer engine 138ccs, not 50ccs
http://www.whizzermotorbike.com/NE5Brochure.htm
You must be referring to some other engine.
As for the comparison- I will put my 49cc 4 stroke up against a 48cc 2 stroke on power- and I dare say, some 69 cc engine. In theory, 2 strokes have an advantage, but the difference between a Chinese 2 stroke and a Honda 4 stroke is more than how often the plug fires.