1974 Mercury 800 80hp Siphoning Gas

[Ogogo]

My boat sat for a couple of weeks. When I went to pick it up there was a strong gas smell. When I checked the tank it was empty and the vent on the tank was closed. Now I thought that maybe someone siphoned it but, when I was running the boat it seemed to get flooded between stops and starts. After it is running, it runs fine. I started disconnecting the fuel line between stops and starts. Now before all of this I rebuilt the carbs and cleaned the entire fuel system. Any ideas?

 

[DavidMoore]

Difficult to imagine this could happen, but I'm not there so will take you word for it.

The only thing I can think of that would allow siphoning to cause a flooding condition between starts is if both of these are true a) fuel tank is higher than the engine b) your floats are set wrong or are too heavy.

Move the tank so it is lower than the engine and rebuild the carbs again, paying attention to float height and that the floats are not leaking / saturated, or the needles are not sticking.

If fuel tank can't be moved, fit an anti siphon valve to the fuel tank outlet (vital safety equipment on an inboard but normally not needed on an outboard because the fuel tank is almost always lower than the engine). In fact if not fitted, fit an anti-siphon valve anyway, it may be required by legislation where you live.
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More likely someone stole your fuel, or you have a leak in a part of the fuel system that is lower than the tank.

Possibly the enrichener valve might be stuck open causing flooding between starts and rich condition.

 

[SoCalBoatGuy]

Hole in the gas tank?