Linhai 257 cc Need Help Removing Vacuum Nipple From Head  By  bob123456789 (Read 1,616 times)

manifold vacuum is the highest with a closed throttle (idle).
the valve/pump operates the best at idle.
as you increase the throttle, the vacuum decreases, your pump/ valve becomes less efficient.
by the time you reach WOT, manifold vacuum virtually vanishes, rendering your pump/ valve inoperable

IOW, you will idle good, but WOT cannot be sustained (you must constantly open/ close the throttle).

i tried an electric pump, but it didn't work well for me, i decided to go with a direct feed with a manual shutoff valve.
i had no problems at WOT with this setup.
in using the above setup, you must remember that the gas tank outlet must be a minimum of 6 inches ABOVE the carb fuel inlet.