Weird starting problem

[formula]

Well, a wacky proposal for a wacky problem....maybe your starter isn't putting out as much torque as it should, but it's still enough to just barely turn the engine--as the engine gets going, the angular momentum of the rotating assembly increases and more and more of the torque being generated goes towards increasing the acceleration of the crank, until it finally is moving fast enough to turn over. Instead of it happening virtually instantly, it's drawing it out over a period of time.