I also have a 1750 and attached it to my NTSC C128Dcr to play sonic off an original 1581.
For me, the game wouldn't even load. I assume you're using
v1.1 that dropped yesterday which was supposed to fix the problem. So are you telling it during launch to
not use the 128's acceleration?
I've yet to find a single NTSC hardware combo that works with the Sonic port that's not janky or ultimately broken. I was convinced it needed to be played on either PAL, or FPGA set to PAL, or possibly just using VICE.
I get all kinds of screen garbage, game speeds that speed up and slow down at certain times, and god forbid you press down on your joystick to make him turn into a ball. It'll simply lock the game up (sometimes it will hard-lock the game entirely).
Example.