thanks for the thoughts tkeithlu... I am kind of drifting back to the mounts. Observing the engine through this certainly shows a significant amount of movement. There is no powering through, and if pushed to when the banging starts it becomes somewhat scary. I can usually get it through the rough spot prior to this by back and forth throttle and at some point it just sneaks past, and accelerates nicely after which I can back down to whatever engine speed I want. It has however been getting tougher to get this to happen. The mounts are older, so replacement even if there is nothing obvious is not unreasonable simply from a maintenance
perspective, but the mount expense certainly is daunting. As noted that there is never an issue until a few days after launch which gave me belief the mounts were fine, but after hopefully eliminating centering and alignment issues, propeller
imbalance, as you say...back to the mounts.
As for the propeller, a replacement for the original fixed 3blade, and I followed Flex-o-fold's recommendations based on previous successful replacements
on the same boat
. Shaft dia is 1" and about 3' coupling to cutless bearing.
Oceansailor... not exactly... no evident problem out of neutral or in idle forward ... it is trying to get it throttled up from there that the issue happens.