Welcome to the forum.
First start w/ maximizing your insurance for your loved ones...
Nothing comes to mind that is more flammable than aerosol spray start.
Using that in the engine compartment is super brave, waaay more than I could muster.
Done w/ my superlative sarcasm.
Please stop using spray start on your boat. There should never be flammable vapors on a boat, except contained in the intake manifold on the way to combustion. The human nose is an excellent detector for flammable vapors and once detected the problem should be corrected before usage.
On the plus side those symptoms / conditions all point to a carburetor problem. My guess is the carb might be fine, except possibly has issues related to old fuel obstructing passages, perhaps even the part of the accelerator pump system.
Many times a carb just gets too old and replacement is required. Another option is to enlist a professional for rebuild. My first step is to always try fixing it myself, but that is me...
