Quote:
Originally Posted by JEC3039
Regarding the "small orifice" we've all seen on older 3-port pumps, here's an update for you. The Carter M4690 no longer has the plug in the tubing with a small drilled hole in it. That's gone. The return line port is simply a one-inch-long piece of 1/4" thin-wall tubing welded to the bottom of the main can. Pontiac may have specified a controlled-bleed port back in the day when AC-Delco made these pumps, but that feature is gone from the current Carter pump!
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Wouldn't this significantly reduce flow to the carb? If this pump is rated for a max of 40 gph, it seems more than half would be flowing back to the tank. A high-flow inlet seat orifice in a QJ is about 0.13" diameter... a wide open 1/4" line back to the tank is way less restrictive.
Is it possible the tube extends into the can and ends with a small orifice?
Here's an example I found on the web:
