Hi, welcome to the forum !
I've run several chabers on cycles in my time and want to metion that not only are there low, mid, and high rpm band chambers but there is one called a "torque tube" (which increases the engine's torque all across the rpm band)
Expansion chambers can have a strong abrupt peak spike of power and the best
thing to do with that is go with a lower numeric ratio which will mellow out that
power and stretch it over a wider rpm range.
If you go with the high rpm chamber you'd probably have to gear so you can cruise just below where the tube puts you into the power band. As these motors are one gear ratio that is something to give consideration. But a bolt on
expansion chamber is the simplest way to go to gain performance. Next to that is trying some different gear sizes and do some road testing.
Some of the guys here have found chambers at different pocket bike accessory web sites reasonable or on ebay. The best chamber is one tailored to your engine, although some claim to get performance boost
from something for other engines.