I had that problem and the only way I was able to solve it, was to clean and
lube the bearings. On mine the armature was binding under the force required
to turn the engine well enough.
Hope this helps

On 6/20/07, Mark E. Skeels <meskeels@earthlink.net> wrote:
>
> Ok here's a mystery (to me...)
>
> I've got an old lawnmower with a Briggs and Stratton 2 cylinder 4 cycle
> engine.
>
> The starter motor lacks sufficient torque to start the engine. It
> sputtered and almost started one time, even so, but no success
> subsequent to that hopeful event.
>
> I turned the flywheel by hand and it seems free enough.
>
> I measured the voltage drop and there's about 1.2v total drop in the
> wiring between motor terminals and battery.
>
> I put a new starter solenoid in.
>
> I replaced the brush assembly in the starter motor.
>
> I removed the armature and looked at it; it looks sound and I cleaned
> the armature contacts with contact cleaner.
>
> The magnets look OK to my untrained eye. They are not loose and they are
> not cracked.
>
> I read on the internet that someone had a similar problem, did all this
> stuff, and still had to replace the entire starter motor, which solved
> his problem.
>
> I am about to drop $100.00 on a new starter motor.
>
> Can anybody shed any light on the failure mode? Does this even make
> sense or am I missing something?
>
> Thanks,
> Mark
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