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Fuel pressure from tank causing leak?

Jupiter Dinghy

Jupiter Dinghy

Regular Contributor
A new one for me...... went on the water yesterday, ran the 9.9 Evinrude (1979) hard and long (had fun with a trio of dolphins on the way) and the motor ran as good if not better than a brand new one, came back home, rinsed boat and motor, and forgot to unscrew the gas tank opening a bit as it is building pressure and inflates like a balloon with the South Florida heat.
Left this morning for an errand and lunch, and when I came back around 2pm, I smelled gasoline in the air by the boat. Went to take a look, and sure enough the plastic tank (Attwood) was just about round enough to play soccer with.
So I unscrew the cap, and pressure relief brings the tank back to its original shape, then I go to the back of the boat and see traces of gas / mix on the ground, and the lower unit as you can see here:
98abmr.jpg


After closer look, I found that the gas/mix leakage was coming from two spots, right underneath the power head here:
2znsjdc.jpg


And at the lower prop hub nut here:
akh37a.jpg


A few minutes (maybe 30) after releasing tank pressure, the leakage stopped.

So my thought is pressure build up in the tank flooded the engine and pushed fuel hard enough to get it to overflow in the engine housing, and leaking through lower cowling and exhaust shaft...
Is that possible? Has anyone experienced this before? Should I be looking for another gas tank?

Thanks as always for chiming in.
 
Last edited:
Jupiter Dinghy said:
thanks for the response.... so what happened to gas caps with built in safety valve that allows pressure relief automatically?..... or am I a dreamer? :)
Click to expand...

The new fuel tanks only vent when the pressure gets too high. You need to install a Fuel Demand Valve in the fuel line between the fuel tank and the primer. This valve keeps the pressure in the tank and does not allow the tank pressure to push fuel past the float needle valve in the carb. When the engine pulls a vacuum on the fuel demand valve, the valve opens and lets fuel through.

You can thank the idiots at the EPA for this.
 
Tilting the engine changes the carburetor float level angle which in turn allows the float needle valve impossible to seal off the fuel flow, a normal happening.... loosen the fuel tank cap or disconnect the fuel line from the engine.
 
joereeves said:
Tilting the engine changes the carburetor float level angle which in turn allows the float needle valve impossible to seal off the fuel flow, a normal happening.... loosen the fuel tank cap or disconnect the fuel line from the engine.
Click to expand...

Will do, thanks Joe.
I wonder if any of those things ever exploded after being left in hot sun for days......?
I guess the fuel intake plug could pop off from too much pressure eventually.
 
Docksidemarineservices said:
The new fuel tanks only vent when the pressure gets too high. You need to install a Fuel Demand Valve in the fuel line between the fuel tank and the primer. This valve keeps the pressure in the tank and does not allow the tank pressure to push fuel past the float needle valve in the carb. When the engine pulls a vacuum on the fuel demand valve, the valve opens and lets fuel through.

You can thank the idiots at the EPA for this.
Click to expand...


The new fuel tanks only vent when the pressure gets too high. You need to install a Fuel Demand Valve in the fuel line between the fuel tank and the primer. This valve keeps the pressure in the tank and does not allow the tank pressure to push fuel past the float needle valve in the carb. When the engine pulls a vacuum on the fuel demand valve, the valve opens and lets fuel through.

You can thank the idiots at the EPA for this
 
Docksidemarineservices said:
The new fuel tanks only vent when the pressure gets too high. You need to install a Fuel Demand Valve in the fuel line between the fuel tank and the primer. This valve keeps the pressure in the tank and does not allow the tank pressure to push fuel past the float needle valve in the carb. When the engine pulls a vacuum on the fuel demand valve, the valve opens and lets fuel through.
Click to expand...
Thanks
 
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