Points are too tight, should be gapped at .020. This is printed inside on the magneto backing plate.
I tried looking up a J17L plug, but could not find any specs on it, but if it is a champion, 17 heat range is really hot. I have used Champion J8C with success.
My preferred spark plug is Autolite 295.
Did you take a compression test? You should have at least 70 lbs of compression.