[Formulajones]

Originally Posted by Shiny

My memory is suspect, but I recall reports of new aftermarket pumps delivering pressures higher than claimed when I shopped for a pump a couple years back. If true, then you are not alone.

I had fear of pressure then, as I was chasing a flooding issue and didn't trust my needle and seat to hold more than 6 or 7 psi.

Are you sure your symptoms aren't just what happens when fuel flows into your carb bowl(s) when the needle and seats are closed? If you mash it a few times, the inlet needle(s) should open and the pressure should drop a little. When the floats rise and shut it off, the pressure should reach the "max", right?

3 Carter short can pumps listed for 68-72 (M4868, M4690, M4885) all "spec" a max of 6 psi and a minimum of 5 psi, with a minimum flow of 40 gph.

Yours is definitely higher so will be interesting to see if a replacement corrects it. Basically, is yours a manufacturing defect or is it a design that doesn't deliver what is claimed?

As to the 3-line vs 2-line, Carter doesn't spec either one differently. The M4868 with 2 lines is spec'd the same as the M4690 and M4885 with 3. As I understand, the 3-lines don't allow much flow... basically a small orifice to reduce vapor lock. To me, this means I wouldn't expect them to deliver lower or even more steady pressure than a 2-line pump.

We would all not be guessing if Carter or any other brand shared data. I asked for pump curves and was told "no" by Carter, Delphi, and GMB.





I was on that thread and envy this story. What pump do you use that has zero leak-back? I want one!

Mike

That particular car uses a Holley mechanical pump. Now that I think of it I believe it's the summit version of that. I'd have to go back to my purchase history but almost positive it's the summit branded version.