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Some portable inverter generators have three run settings on the control dial: off, fuel off spark on, and fuel on spark on (if you don't count choke as the fourth setting, if the choke is a separately controlled valve).

However, some generators have only two run settings: off, fuel on spark on.

Since generators generally use carburetors apart from some rare expensive fuel-injected models like Honda EU32i, they suffer from the problem that the fuel in the carburetor might go stale. Therefore, the benefit of a "fuel off spark on" position is massive, it allows running the carburetor dry from fuel without running the gasoline tank dry from fuel. If the fuel tank is sealed (by turning off the fuel vent), gasoline there could stay useable for months, or even a year with a fuel stabilizer.

However, I happen to have a generator that doesn't have a "fuel off spark on" position. It does however have a separately controlled fuel tank vent.

I was thinking that if I turn off the fuel tank vent, maybe the negative pressure that builds in the fuel tank would prevent the carburetor from getting more fuel from the fuel tank. It might allow running the carburetor dry from fuel, without running the fuel tank dry from fuel.

So if I turn off the fuel tank vent when the generator is running, would that effectively work as the missing "fuel off spark on" position of the control dial? Then when the generator turns off from missing fuel in the carburetor, the control dial could be turned off to prevent fuel from getting to the carburetor ever again until the control dial is turned on.

juhist
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2 Answers2

8

Your fuel tank vent valve is likely designed to stop evaporation, not to cut off fuel flow to the carb. You can try experimentally, but I think you'll find that the generator will run until the tank is empty even with the vent closed.

This is because gasoline has a significant vapor pressure. The vapor pressure depends on the temperature and blend (summer/winter), but I've seen it reported anywhere from 4 psi to 62 kPa (about 8 psi) at typical temperatures.

If the generator has a closed vent and you use enough fuel to drop the pressure in the tank a bit, the pressure will be immediately made up by evaporation and fuel flow will continue.

To achieve your goal of running the carb bowl dry, you can install an in-line valve in the fuel line. These are widely available as replacement parts for outdoor power equipment.

MTA
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Messing with the tank vent isn't a good idea. The vent is meant to equalize air pressure, if you close it you will cause a vacuum in your tank which could cause it to distort. You don't want to chance damaging your tank! Install an in-line fuel line valve as @MTA suggests instead.

GdD
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