I have both it excellent shape, the z50 will walk all over the trx70 in every way. I understand weight, rotational mass etc..but differences aside, one would think the 72cc could either out perform the 49cc low end OR top end. Especially since the trx70 is a 4spd. They are geared near identical except for the 2nd gear on the trx70 is slipped in between the z50s 1st+2nd. I was hoping to see what others thought about this.