David Nebenzahl wrote:
dpb spake thus:

David Nebenzahl wrote:
...

....
...At slow speeds, it feels like it's "chugging" or cogging. ...

If it runs and variable speed is functional, it isn't a simple wiring
problem. The spitzen-sparken and erratic running at low speed is
indicative of the brushes not fitting correctly. I'd hazard a guess
the combination of "cleaning" the commutator and perhaps turning the
brushes around or otherwise getting them mis-aligned is the primary
problem...

Then you'd guess wrong.

Reread my original post. The drill runs without *any* sparking at low
speeds. ...

It also runs (as the _retained_ quote _from_ your original post shows)
poorly. A very good description, in fact of what poorly fitting
brushes or damaged/rough commutator edges act like.

Was simply trying to point out an area that seems more likely than
miswiring, but if you know better then fix it as you see fit.

....
BASIC ELECTRICAL PRINCIPLES (which I do know):

Are drills like these wired with the field and armature in series (as it
is now) or in parallel? Simple question. (Sorry for shouting above!)

Then you obviously must know how motors work and have the answer to
your question available by applying same.