Nobody has addressed the real problem & that is: the starter being used is under powered. Just like the engine the starter is trying to start, a starter has a HP rating. The P/master 9513 is only 1.8 hp. Might work.....might not. If you want to ensure that the engine starts under all conditions, you need a 3.0 hp starter.
MSD dyna force are over 3.0 hp
CVR #CVS-1338M is 3.0 hp
Power master ultra tq #9413 may be 3.0 hp
Tilton also have 3.0 Hp starters.