Sometimes thes motors tend to be harder to turn over when they are warm. My 216 is one such case because I shimmed the main bearings with the minimum possible clearance. I would try turning it over by hand when it is cold and then when it is hot.
Another thing to look at is the size of the cables. There are a few posts on that. Also if the timing is too advanced, it can cause problems. You can check for this by turning it over with the ignition off.
