I think 100-1 engines are as I understand it largely the same mechanically as 50-1 engines, but specified 100-1 to reduce emisssions. (I had a 100-1 yamaha and was told to run it on 50-1 for heavy wide throttle use and only 100-1 for pottering about).
50-1 on a 100-1 engine is unlikely to foul the plugs, and will probably reduce engine wear.
I would double check you have the right spark plugs, and use only a good low ash marine grade 2stroke oil.(quicksilver)
(may be teaching granny to suck eggs but some people do use car engine oil or bike aircooled 2ST oil
I would also check the choke is fully returning to fully open.
other than that give it more beans
only other thing I can think of is we had a fleet of hire boats with 9.9s on and people used to flood them. we always used to thell them one pull with the choke out, then shove it in. more often than not they would give 3 or 4 pulls on full choke and flood the engine. it would then take 10-20 pulls with the choke in and throttle as open as possible in neutral to clear.
perhaps all merc 9.9s are really prone to flooding if slightly over enthusiastic on the choke?
Also try stopping the engine by disconnecting the fuel line, so when you pick it up to transport it you dont empty a carb full of fuel into the crank case