Concerning hard turning on compression......hopefully it could just be timing check that out first...... but it could be this.....it is called automatic compression release (ACR)....on your cam gear there are weights and a very fine hairlike spring. For starting the weights allow the exhaust valve to remain partially open to reduce compression so the starter doesn't have to fight it. As the engine starts rpm's build and centrifical force pivots the weights away from opening the exhaust valve. The before mentioned hairlike spring pulls the weights into position when the engine is not running so that the weights can do their job for starting. You said this is a newly rebuilt engine so I would look for the spring to be broken, weak, or out of position on the weights. You can view the cam gear, the weights, and the spring by taking the cam gear cover of of the side of the engine, just below the carb. It is very tight quarter but if you can see that the spring is out of place you may be able to get it back where it belongs. But check the timing first!!!!
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