Update and final resolution. Spoiler Alert - replaced carb.
Fuel leak at fuel pump (apparently - could have been fuel line at pump) and chronic flooding led to the following:
-Replacement of fuel pump diaphragms and gaskets
-Replacement of carb gaskets, float valve, rubber seals and caps (all the cheap and easy stuff). These just because it was easy and I had the carb off anyway.
-Soaking carb in carb cleaner
-Replacement of fuel lines
Result - motor would start and run, but only with choke half on and throttle half up. Anything less on either and motor would die.
Opinion of a local shop was that I had not cleaned the carb properly.
Having spent a good deal of time, I decided to cut my losses and just buy a new carb. $188 seemed a bargain based on labor estimates at one local shop.
Outcome - new carb solved all my problems. Starts easy, no flooding, idles nicely.
Takeaway - carbs can be finicky if you don't know what you are doing.
Anyone need a parts-only carb for a Tohatsu M8B? Cheap!