Nathan - In my understanding of those filters, they were originally designed with an orifice restriction that allowed for vapors to be purged back to the fuel tank through a return line to the tank. If there was no vapor to purge, it would allow a minimal amount of fuel to be pushed back to the tank through that return line.
I haven't found anything that gives specific details about how that bypass may affect fuel pressure levels at the carb inlet, but think you would need to be able to determine that to see if your fuel pump is still able to provide the necessary flow/pressure with the constant bypass. If it allows too much pressure/flow bleed off, your pump might not provide enough fuel for the engine to run properly.
I came across a thread in an
AMC forum that discussed much on the bypass filter that you may find interesting to read to help answer your question.
