It might be a timing issue. I noticed the same behavior with my '28 four banger. The fix (for my problem) was to make sure that when trying to start the engine, the spark happens at TDC, not before.
If the spark happens before TDC, the explosion is pushing AGAINST the starter and the starter has to push through the explosion. If the spark happens AT TDC, this 'push back' is not there and the engine turns over nicely.
Hope this helps. Dean
