Vented fuel tank query.

VMAX  Forum

Help Support VMAX Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Adie Porter

Oct 7, 2018
Reaction score
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.
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?
Am i looking too deeply into thia?


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.
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

Latest posts