[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.

Originally Posted by Formulajones

....

Another interesting tid bit because we were on this subject a while back, is cold starts, with what some consider too much cranking using mechanical pumps.
This car will hold fuel pressure after I shut it off for days and days, even weeks. When I explained my cars start rather quickly with mechanical pumps even after sitting for weeks I believe this is the reason why. I don't have drain back or fuel leaking issues that I believe must be going on with other examples.

In fact when I jump in and see 8 lbs. on the gauge before I even crank it, I can watch the pressure drop a pound every time I pump the gas as the squirter shoots fuel. As soon as I start cranking it's instantly back up to 9 lbs. and fires off within 3-4 revolutions after sitting for weeks.

Lost track of that thread but anyway thought I'd share.

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

Mike

[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.