Belt adjustment on edgemaster 800, 120 Honda engine.

[Ryscurbing]

Just bought a new setup from a guy. Just testing out machine with wet sand and it gets stopped up with small shovel fulls. Belt just squeals. I've adjusted the plunger head every way possible and still same results. Anyone got any suggestions? Or know the belt size so I can get another because I can't see a way to tighten or loosen the belt.
Thanks