You can get a lot more out of this engine by removing the baffle in the muffler. Look down the exhaust outlet and you will see the head of a pop rivet. drill it out carefully and you will release a aluminum disk in front of it . The disk is a restrictor that was intended to keep noise down. ( It really keeps power down) You will pick up a lot of RPM's for sure.
The disk can be driven forward to the exaust inlet port where you will get the full picture. Using needle nose pliers you can bend and crimp carefully until removal is accomplished. Avoid scoring the inlet as it must fit the header pipe. This is easy to accomplish, will still provide ample pressure for fuel feed and really does not produce offensive noise.
I have a G-75 and a G-90 that have the treatment.
The G-90 is on my UCD 46 a nice match as the ST's are so light.