Slow Crank, No Start When Warm

A voltmeter AT THE battery will tell you that as well. That is part of the reason I emphasize voltage checks. Crank the engine cold and hot, with your probes stuck into the tops of the battery posts. If the battery is known to be charged, and the voltage sags anywhere near 10V or lower, have it load tested. By someone with a CARBON PILE tester, not a shirt pocket instrument. The battery could be somewhat discharged, old, defective, or too small.

If the battery load tests OK, but the V AT the battery still sags when cranking, then the starter is drawing too much current. This could be something in the engine bad-- drag, bearings, etc, bad starter, and possibly small cables.

Something I did not see mentioned is we were talking about too much timing advance. Easy to check for that. With it hot and showing the "slow" problem, ground the coil wire or otherwise disable the spark. If it spins up nice then too much advance.