I have never seen a specific PSI, but I think they bypassed at about 10 PSI. We retrofitted them to older vehicles here in Texas. During hot weather the fuel would expand in the fuel line between the pump and the carb after the engine was turned off. The needle and seat could not handle the pressure and the carb would flood when you tried to start it again. The bypass does not come into play while the engine is running. The fuel pump or an after market pressue regulator regulates the pressure while the engine is running.
Thanks, Ken. That’s more or less the scenario I’m trying to solve. Doesn’t happen all that often on my truck, but I occasionally get a failed hot start I have to overcome by pulling the hand throttle wide open.
It’s cheap insurance and I don’t see much downside. Return side plumbing would already be done if I wanted to go a step further and do a bypass pressure regulator.
That AMC thread Dan linked is an interesting read. Sounds like the filter they are discussing bypasses A LITTLE fuel all the time, when you get one that’s made correctly that has a restricted orifice. But some of the recently made offshore versions and just a wide open 1/4 inch secondary outlet. Thanks, China.
I’m probably gonna buy one, US-made if I can find it, and do a little inspecting and testing before install.
