[geezer#99]

if Your timing is too far advanced you start the burn too soon. The piston is still rising at that point and the combustion process tries to push it back down. The starter has to work harder to push the piston up. When the starter works harder it creates more heat. More heat in the starter makes it turn slower.

2. It doesn’t take long for the starter to cool off enough to crank better. In your case about the amount of time to plug the wire back in.
Your timing’s likely close. Pull it back a couple degrees.