Not necessarily.
It's all a matter of leaking fuel putting explosive gasses in the engine compartment. Then you have spark from the dizzy, the starter or the alternator that sets it off. That's when you get the fire. Whether that happens at startup, idle or WOT doesn't matter. You don't want it happen at all. Closed marine engine compartments have no place for raw fuel fumes to go except sit in the bilge waiting for a spark and the reason for a bilge blower that should be used before every engine startup.
Auto's don't have that problem. Raw fuel leaks dump on the ground harmlessly and evaporate away. Usually. But fires still can and will happen.
Marine carbs have sealed throttle shafts and "J" vent tubes to dump any excessive raw fuel down the throat of the carb and into the engine. It'll flood the engine but won't dump raw fuel into the bilge. Auto carbs don't.
In the event of a diaphram rupture, marine fuel pumps route raw fuel up a separate hose to the carb for the same reasons I just listed. Auto fuel pumps don't.
Marine starters and alternators are sealed for spark suppression. Auto units aren't.
Marine dizzy's are vented with screens that act as mini flame arrestors just like on your carb to prevent sparks. Auto units do not.
These are the reasons that Marine rated parts are considerably more expensive and the average guy...aka, cheap ass....has no idea why so they figure it's OK to just put automotive parts in it's place.
So your automotive substituted parts may work fine and probably run for years without an issue and nobody is the wiser. All in the name of saving some bucks. All it takes is one isolated freak accident to totally ruin your day, your life or someone else's life. So you have to ask yourself....How many dollars is it worth that would possibly prevent that one freak accident?
