AC Fuel Pumps on '69 Z28

[COPOZ/28]

I've had two different AC fuel pumps on my '69 Z28/302 (all OE spec engine, carb, etc.).  One pump has the "AC" logo cast on both sides of the tower and has the following ID stamping on the mounting flange: 043V40987.  There are no other ID stampings.  I ran this pump for a number of years and replaced it about 6-7 years ago -- it was running fine when removed.  The AC pump I then put on does not have the "AC" logos cast on the tower and it has the following ID stamping on the mounting flange: 40987.  There is also a faint ID stamping on the opposite surface of the mounting flange that I believe is: 059. The 0 and the 5 are very faint but the 9 is a much deeper.  I am 99% certain neither of these two pumps is the original.  Can anyone confirm what these pumps are in terms of correct replacement, or generic, or

And now to my concern:

When this second pump (no AC logo, 40987 + 059) was on the car, I found I had to a adjust the float level nut down quite a bit -- almost to the point of running out of threads, in order to set the wet float level, engine running, to dribble out the sight plug holes.  After being set, the float bowls were removed and the "dry" float setting checked per the '69 Chevy Service Manual spec's of: "Invert bowl and insert 0.350" drill bit Primary or 0.500" drill bit Secondary between float and top of bowl and adjust to achieve specified clearance."  Checking both bowls, I found the float level in each about an additional 3/32" to 1/8" lower (meaning "down" in car position)than these spec's of 0.350" Pri/0.500" Sec.  This lead me to believe this second pump (no AC logo 40987 + 059) was putting out more than the 5 - 6.5 psi spec the Service Manual calls for.  I never checked this same "dry" float spec when I had the  first pump (AC logo, 043V40987) on the car years ago and set the float level with engine running.

This week, I built a test fixture, with a rotating eccentric on a shaft, driven by a typical 3/8" drill motor.  I can bolt fuel pumps to this fixture and run supply and output fuel lines to the pump to feed fuel to the pump from a small gas can at the same level as the pump and run the output fuel down into a 2nd gas can.  The output line has a small valve I can either close or just barely open in order to have a minimum of fuel flowing through the pump and gauge system and develop pressure.  I also mounted a liquid filled pressure gauge to monitor the pressure the pump achieves.  The results of testing these two pumps are:

The first pump (AC logo, 043V40987) = 3.5 PSI
The second pump (no AC logo, 40987 + 059) = 6.0 PSI
(I also tested a 3rd pump, a new Carter p/n M4685, made in China, their '69-'71 302/350 Hi Perf repl pump = 6.0 PSI vs spec of 5-7 PSI)

I'm surprised the second pump put out only 6 PSI, well within the Service Manual spec of 5 - 6.5 PSI -- I was expecting something higher, given how far down I had to adjust the float setting nut on both bowls.

Could this be a needle/seat issue that required running the float nut down to almost run out of threads with the 6 PSI pump, even though the pump pressure is within spec?  I use only genuine Holley parts and had replaced both needle/seats at the time the second pump (6 PSI) went on the car about 6 years ago.  The float settings were set back then, engine running, dribble, and never changed, just re-checked occasionally with no re-adjustment ever required.  I suppose it's possible the two new needle/seat assy's I put in back then could have been a bit out of spec -- what else would be something to try to get a more "normal" float setting?  I might just put the first pump (AC logo, 043V40987) that tested at 3.5 PSI back on the car, but having been run for a number of years and then sitting on the shelf, I'm concerned the pump's diaphragm may have "dried out" and could fail rather quickly.

I may be chasing an issue that really isn't one, but I am curious.  I haven't seen this "low" of a float position on the many other 4150/4160 Holley's I've played with over the years.  Thanks for any wisdom provided!
Chuck

[GMAD_Van Nuys]

I've always used the procedure below to set the float level on Holley 4150 carburetors:

https://www.youtube.com/watch?v=ge-mIk6nEYQ

Do you have the same problem adjusting the float level with the Carter M4685 fuel pump?

[COPOZ/28]

I haven't yet started the car up for the first time this spring (I live in northern Michigan), so I'm not able to tell you if the new Carter pump results in the same float level as the no logo AC pump.  I hope to finish my spring "to do" list in the next week or two and then fire up the engine.  I'll report on what I find at that time.

[GMAD_Van Nuys]

My 1970 BOSS 302 still has its original Carter X 4910S fuel pump, which was rebuilt.  I find that the gasoline will evaporate from the carburetor if I don't start the engine every couple of weeks.  I know that some will remove the sight plugs and fill the bowls with gasoline.  I'll just let the car sit for a few minutes if it won't start after a number of attempts and usually it will start with one turn of the starter.

I had a 650 cfm Holley 4150 with mechanical secondaries on my 1966 Mustang and never remember having a problem with the float level
Even with a Le Mans camshaft, it would only rev to 7000 rpm, no match for my friend's 1968 Z28!