Is the cartridge version NTSC compatible?
There's only a PAL cartridge for Sam's Journey on the C64. You can run the PAL cartridge on an NTSC C64, but the music will be too fast and you'll experience a lot of slowdowns and visual glitches.
Do you happen to have a NES as well? Then you might want to try Sam's Journey on the NES for which a proper NTSC cartridge is available: