It was probably your compression tester that was the culprit.

The cheap ones use a heavy spring in the guage checkvalve that requires about 40psi to overcome the load of the spring and open the port to the guage. That would make your reading 40psi lower. Also, the Aprilia and Suzuki (same engine) run a lower compression ratio that would make your readings lower. Most I have tested are around 90-100 psi.

My NSR pulls about 115-120psi with the overbore. It was about 110 on the stock cylinder setup.
_________________
Paul Herr
2000 Honda RS250
1994 NSR250SE, far from stock.