Re: sbp expansion chamber?
All you have to do to tune it is first have the motor running well BEFORE you put the pipe on, install pipe, warm it up with a short run, do a full throttle run for approx. 1/4 mile, hit kill switch @ full throttle, let cool, read plug.(this checks the Carb. rich/lean) adjust "C" clip as needed, repeat as needed, (sounds simple and quick, not always) if your close with the carb, you will feel a big difference, since your running a 49cc, they usually rev a bit higher, you may want to shorten, instructions come with the pipe or are on SBP web site.
The weight is just right, not to heavy but durable, I welded a bracket on mine with a MIG welder, no burn thru issues, just don't fall asleep while your welding on it or get a shop to do it.
Hope that helps