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Pop-off pressure, the way we check and measure pop-off, should not be confused with fuel pressure. It can’t not and does not control fuel pressure. The correct fuel pump will not make much more than 1psi of fuel pressure to the carburetor. Therefore, 10psi of pop-off pressure does not mean 10psi of fuel pressure nor does it mean the fuel pressure must overcome 10psi to open the needle valve.
Pop-off pressure is based on the type of inlet tension spring and its install height.
The latest Tillotson Springs come in with a spring pressure weight for the HW Tillotson Carburetors
24B-345 Tillotson Inlet Tension(Pop-Off) Spring is a 48g spring