Not sure but in the past I used masking tape to check for rubbing. Does you motor have a removable points cam? Look to see if it is cracked maybe? Is this motor the common magneto set up? I’m lost with the newer systems. The downward pressure is changing something.
Edit: Measure resistance from plug wire to ground please, before & after tightening. I too have had problems with bad ground to block from the mag plate, Again measure resistance before & after adding a test jumper to ground. Does the plate turn easy after tightening? Did you check resistance on the points closure? Just my .02,
