If you are taking paying passengers on board it changes the picture.-------Contact the local ---Power Squadron ---- Coast Guard----To see what is required.
Hard to believe that these new 4 strokes are not well supported.----One stroke against Yamaha I guess.----Many folks will be disappointed by modern corporate policies !!
When engine was rebuilt did you hone out the cylinder and then install a standard bore piston in #2 hole ??----We are now over 200 postings on this project / motor.
Post the compression values taken today.-----Inspect reed valves.----Take carburetor apart and post pictures of all the gaskets / parts.-----Stop running this motor until you sort out the issue.
Nobody can see what you are doing.----That is why we ask questions.----I have never had an issue getting one of the crankcases apart.----Have done more than one !