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Old 09 July 2010, 11:15   #1
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Gas Tank Pressure Valve

Does anyone know if the pressure release valve should be open or closed when running an outboard?

Regards

Adam
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Old 09 July 2010, 12:49   #2
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the one on the fuel tank needs to be open ,
,otherwise the fuel will stop flowing due to a vacume forming when the fuel starts getting used up and their is no air going into the tank airspace to replace the used fuel .

After checking for a loose or not fitted kill cord one of the first things to check for in the event of an outboard engine stopping or not starting ,
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Old 14 July 2010, 16:52   #3
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Personally have forgotten to open the air valve several times while sibbing for hours and the engine didn't stop once!! Probably Tohatsu tanks/engines don't have this sort of issue.
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Old 22 July 2010, 04:23   #4
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Quote:
Originally Posted by Locozodiac View Post
Personally have forgotten to open the air valve several times while sibbing for hours and the engine didn't stop once!! Probably Tohatsu tanks/engines don't have this sort of issue.
a lot can depend on the air /fuel tempreture and how full the tank is and how much the tank will flex ,in warmer climates the air pressure can build up with the heat from the sun forcing the fuel down the pipe making the engine run for a good while ,
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Old 22 July 2010, 04:44   #5
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Quote:
Originally Posted by Locozodiac View Post
Personally have forgotten to open the air valve several times while sibbing for hours and the engine didn't stop once!! Probably Tohatsu tanks/engines don't have this sort of issue.
Loco,

I think that is more to do with the size of tank/engine you have than its brand. Possibly combined with the effects mart talks about relating to heat.

I've managed 3 hours with a 20HP yam, a 25L nearly full tank before the engine started complaining. By that point the problem was obvious when you looked at the tank as the side walls had been "sucked in" so they were slightly concave. I'd probably used less than 10L of fuel. Small engines use less fuel therefore last longer before they create sufficient vaccum. The 25L (ish) plastic tanks are quite flexible so deform which "reduces" the amount of vacuum formed. I've seen tanks both "sucked in" and "blown out" from temperature changes. If yours doesn't do this perhaps there is a small leak somewhere.
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