How much fuel or water, for example, can a needle and seat float flow in an hour, with different pressures, If you have 2 needles and seats like with a Street Demon, or most Holley style carbs, you can just double the amount off gallons it shows To get the flow per second just divide the total by 360.


https://www.tlv.com/global/US/calcul...h-orifice.html

 

That will calculate the flow rate for a plain orifice, like a carb jet. The problem with a needle and seat is that the needle is an obstruction in the flow path. Depending on the float level and how much force it is applying to the needle, that theoretical max flow number will be reduced. The needle effectively increases the pressure on the outlet side of the orifice, so P2 would be greater than atmospheric.

 

Right, but playing with the calculator should give anyone an idea how pressure effects flow volume on a needle and seat rather than the true flow. Espeacialy in racing conditions. This is mainly handy when ru8nning an auxiliary electric pump, by (my favorite), or in the tank

To get closer to true flow numbers you would have to actually build and run a test rig simulating lines and pressures and any filters, with the carb on the end, with the floats tied down, and then time it. Safer to do with diesel or water. Or just you could try different pressures, and see if it solves any fuel flow problems only under high demand.