I normally run my VMC in the A I, II & III range giving me 560, 1370 & 2100 rpm as it only requires slipping one belt. I have run mine at 190 rpm though and have never altered the pulley or motor mount so it must have been ok. I have changed one of the belts on mine though as it was pretty poorly made. I took the old one along to a local motor factors who managed to supply a fan belt the right size. I've also used Halfords in the past for drive belts! Let us know how things turn out.