Vented fuel tank query.

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Adie Porter

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Hi Guys, im swapping out the carbs and airbox for a top tank and flatslides.
Fuel cap in the fake airbox cover.
What im interested in finding out is, do i need to vent the tank or just use a vented cap?
I am looking for the flush harley style push in to pop up filler cap. How much venting is needed if the carbs are sucking the fuel down, also im in a hot climate and the fuel can expand.
 

Adie Porter

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I dont have to calculate what fuel is being sucked out and compensate with a particular dia of hole for air flow in? Am i looking too deeply into thia?
 

MaxMidnight

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Am i looking too deeply into thia?

Possibly.

I doubt (but am happy to be proven wrong) that as long as the vent hole is (say) 1 - 2 mm that would be sufficient.
I doubt that the volume of fuel drawn even at full throttle is so big that a small hole will allow the ambient pressure to be maintained.
 

Fire-medic

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I used a small drill bit and got a rough measurement of the OEM gas tank vent dia. which is 0.8mm or 1/32".

VMax gas tank vent 0.8mm.jpg
 

Fire-medic

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Goood morning- What does one do about repairing or replacing the fuel cap rubber . thanks wayne b
 

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