The weight of the larger diameter piston... The more the weight, the slower she'll rev. I agree with what you are thinking, I did too. In a 4 stroke car engine, a short stroke and a larger bore equals higher rpm's, but in these motors it is almost opposite. I am thinking it has something to do with the low torque output of the smaller displacement 2 strokes. Or maybe something to do with port volume and timing? I don't know. If these motors had a camshaft I could tell you all about it. I am by no means an expert with a 2 stroke...
As was mentioned before, the last thing an on road car needs is more torque. It will barely be able to keep the back tires hooked as it is. I would think in an onroad application, a smaller bore and higher revs would be about right. Maybe a nice race ported? Usually they are designed to apply the power in a smooth linear fashion, instead of slamming all the power it can out of the hole, such as a 29 or 30.5cc.
The big bore kits were made originally for scooters, with little rich kids on the back of them and we just adapted them for r/c use. So, they were designed to move large amounts of weight, not a 25 pound car with decent gearing.
Trip..