Yep, when you build the motor up with high compression and that displacement, like trying to start a Cat D8 with a Yugo starter (why the old D9's had pony motors to start them), going to have problems until you do install compression releases so the starter has at least a fighting chance of getting the motor turning in the first place past the compression strokes, so motor can spin enough to fire and close the compression release once it does start to run.

Items like ignition timing pull until 600rpm will help with kick back problems, but not going to solve the problem of getting the motor turning in the first place when it up against the compression stroke and no compression releases in play from a dead start of trying to turn the motor in the first place.
Worse yet, you keep sending power to starter at it dam near or stalled out, and all your going to do is burn up windings on the armature from it just being a dead short with it not spinning, or slow spinning instead.

 

https://www.wimmercustomcycle.com/co...elease-kit.php

 

Oh fu*k no !!! Those are trouble waiting to screw you. Thread in here somewhere where a guy was wanting them. Some months later he had the moxie to come back and show the carnage after one let loose, cutting the plug and the head up along the groove on the long plug threads. Looked somebody took a plasma cutter to it.

 

Oh ok, I was thinking for diagnostic test before to make sure that was the problem.