Starter problem...

[Chevelle454]

When my truck('72, 350) has been sitting for a while and the motor is cold, it will turn over and start just fine. But no matter how long I let it run for, even just 10 seconds and then I shut it off, when I go to start it back up the motor will kick back and backfire and the starter will skip and grind on the flywheel. I have the starter shimmed good.

What would cause it to do this? I know the timing isn't set, it's right around 0 degrees. But would that matter for hot vs. cold engine starting?

Thanks in advance,
-Scott