Carrier staring question/problem

[Bruce Parker (RIP)]

Thanks all. The battery seems OK and I gave the ground a little work. But the second part of my question is why the faster cranking with an ounce of gas down the carb? There's a marked cranking speed difference before the gas (slow) and almost 12 volt-ish (fast) once the gas is in the manifold. Is it lubrication? (doesn't make sense) Vapor or pressure? Part ignition on one or more cylinders helping the starter along? (yet there is no sound of firing until it fires up on all eight)