Yeah that’s horrible performance for a kit and pipe, you should be at 45 mph at least!
Putting a bigger carburetor on it is not gonna do nothing if you have the stock 14-15mm ID intake
My stock cylinder revival (basically the same bike as a streetmate) Goes low to mid 40s with my 205-210 lb on it and that’s with no kit.
I’ve opened up the intake tract a little bit more and now I even got more low and takeoff then in the above video,
You need a retune/rejet your carburetor, run a metal mesh air filter, put a 24 tooth sprocket on the back, case match the kit to the ports in the engine block, open up the intake hole to match intake if smaller then intake, there’s a few other things you can do too but that’s a good start