I have an old Clarke motor (1/5 HP, 0.15 KW, 240 v, 1.8 A, 1400 rpm,
type 5DB, single phase according to the rating plate,) that only runs at
400 rpm whether loaded or unloaded. I am looking for suggestions for why
it is slow, and how I can rectify the fault.
My inspection of the motor reveals that:
 It has no brushes so I guess it is an induction motor.
 It has a 8 microFarad external capacitor which suggests it is a run
capacitor not a start capacitor from what I have gleaned from the internet.
 The bearings are not binding or rough, and the spindle is free to turn.
 A cheap multimeter test of the disconnected capacitor gives a
gradually increasing resistance up to 20 ohms.
 A cheap multimeter test of the windings from the capacitor terminals
reads 58 ohms.
Any clues folks?
Possibly a permanent split capacitor motor and those, as well as shaded
pole motors, can be speed controlled to a degree by varying the voltage
so maybe the motor is somehow getting supplied a reduced voltage.
I was just wondering if you had checked the supply voltage at the motor
terminals. It used to be that Machinemart sold single phase motors were
all PSC motors so not a good start-up torque but good for some applications.
I am not an electrician and don't have any known resistances. The meter
is auto ranging so I can't answer your second question.
I shall order a new capacitor in the hope that it will solve the
problem. If it doesn't, the motor is destined for the bin as I don't
intend to spend any more time on the job.
Thanks for your help Andrew.