I am pretty sure that the compression release is derived by way of a small bump in the grind of the exhaust valve. If you have the plugs out and the valve covers off, turning the engine slowly by hand back and forth, and pressing down on the exhaust rocker arm, just around the the TDC area of each cylinder you should be able to feel it. It is so slight you probably can't see it. If that seems good you might want to revisit the starter.
Here is a link to same problem on another venue that might be helpful.. Be sure to read to end (2 pages).
https://www.tractorbynet.com/forums/...n-release.html