If the rotor starts ok, then stalls randomly I doubt it's the capacitor.
Replacement caps - bigger isn't better so stick to the same capacity value
(or close to it). With a test jig in line and measuring motor current
while different caps are put in the circuit, it is quite apparent that a
larger value of the capacitor will increase the current flow drastically.
With the rotor running fine with the proper cap, adding another cap of the
same size caused the rotor to stall and/or become very sluggish.
Here anyway, most available motor starting caps are for 120 or 240 vac and
a value in 120 -140 mfd range isn't common, most are much smaller.
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