If the belt is tight then you may have to take the clutch apart and clean it. Back the screw out on the clutch knob, unscrew the knob and take the 3 tab washer out noting which way it's facing, it does make a difference. Clean everything well, oil and put it back together. If you still have trouble, it's possible someone before you put the washer in backwards.
Rodney
EDITED due to didn't notice Singer in the title at first
Last edited by Rodney; 01-30-2015 at 06:37 AM.