If there are no obvious fuel
leaks, you may be smelling fuel
that has spilled into wood and been adsorbed there. Solvent cleaning and then sealing the wood with epoxy paints
is the best way to preclude or solve that.
But you may also be smelling fuel
from the carburetor evaporating when the engine is off, or the fuel
tank vent, or even a tiny leak from threaded fittings.
As others have said you should not be smelling ANY gasoline, if there is any vapor from any source in the boat, you have a risk of explosion. (And I have nothing against gasoline engines!)
If you clean, check, and recheck everything, use a toothbrush to clean old fittings and crevices, seal bare wood, and make sure the vents are vented overboard and still smell gas...That's not good, it IS toxic and you should not be sleeping with the vapors. I'd try a real thorough steam cleaning in the engine spaces, and adding a solar vent to give the engine spaces a constant positive ventilation out of the boat as well. They're expensive, yes, but I've never heard of anyone willing to give it back once they've installed one.