Hi GordonL.
I'm unfamiliar with this particular IC engine but assume it has two opposing Pistons from your description?
You mention suction through the plug hole on the exhaust stroke I would have expected quite the opposite as you should be expelling the spent gases. Is it a case of " reverse rotation " ?
Is it possible to make a short, close up video of the engine being turned by hand, going through the motions? Pictures are worth many words.
Cheers Graham.