Do you have the version with the shift lever or the one where it's integrated into the tiller-throttle?
I had the latter and it is very sensitive to submersion ..... don't ask ;-) there's dual coils in the housing for firing the sparkplugs: one for idle/low load and another one for high load. I had a fine running engine
at idle or even high rpm
in neutral but one cylinder didn't fire when opening throttle in forward gear
. Multiple dealers took multiple turns to find that one. But I loved the engine
(I had 15hp which is the same as the 8 and 9.9; just the carburetor is different).