> Check that all the clutches lock up. You can do this by hand. If
> they drag it can stall the motor.
It may be worth removing the belt from the motor :
If an air deflector is fitted over the fan remove it by loosening
thw 2 screws between the fan and the motor and removing the
screw on top. Then unhook it from under the 2 screws and take
Undo the 2 screws on the clamps at each end of the motor (2
are the 2 screws refered to above) and lift off the clamps.
Lift out the motor and free the belt from the sprocket. Hold
the belt out of the way (with a bit of wire or something), put
the motor back in place and fit the clamps to hold it. You can
now get the motor running with no load, if there is a problem
in the rest of the mechanism it can't stall the motor.
The motor is fed via 2 pins of plug 4 at the back of the control
unit. You can try disconnecting this to see if the control unit behaves.
According to the diagrams I have, the motor is not powered with
the switch in the 'Off' position. So you may have a problem with
the switch or a shorted snubber network in parallel with it.
There were various motors fitted to the Model 33 over the years.
Some had a current-operated relay to disconnect the starter winding
when the motor was up to speed (and drawing less current), If this
is not closing at switch-on, the starter winding will not be powered, the
motor can't run. The relay is a black plastic box on the mechanism chassis
(IIRC to the left of the motor) with 3 wires going to it.