Why do I have a hard start up and unexpected stalling?

What is your question?

Bought used 4 mos. ago from private dealer. Didn't start having problems until 3 mos. ago with hard start up. Engine cranks but won't catch for a few seconds 7 out of 10 x's. Engine stalling began about 2 months ago, 3 out of 10 x's. Will start right back up. Replaced alternator & battery