Starter failing, battery meter pegged?

[Zed Head]

2 hours ago, RJK said:

the previous owner installed a fuel pump that is quite loud; I don't know if I've ever heard one this loud.

A carb'ed engine would have a low volume low pressure pump.  No reason for it to be loud. 

[RJK]

I have never given my fuel pump a close inspection, as it was on the car when I acquired it, and it never failed. I am now wondering if it may be over-spec'ed for the use. What is the best fuel pump to be running, in you folks' opinion? Should I go mechanical, or stay electrical? the cutoff switch is nice, however I have struggled with some rich running in the past, and won't be surprised if the PSI is higher than needed for 2x original SU carbs. Curious what is suggested, with an eye towards electrical since the wiring is already there. (I run mechanical on my '76 2002, and while it takes more cranking to start if it's sat for a week, it's not a problem for me ultimately).

 

@SteveJ that last pic is, for all intents and purposes, the ammeter reading with battery topped off and car running. the car came off a trickle charger yesterday, and read 12.8V before I started it today. I'll throw a DVM on it soon and get an actual number. And yes, the delta between the needle in that pic and the center line is the fuel pump draw; when i killed the fuel pump at the fuse, it was almost dead on center while running.

Edited October 2, 2023 by RJK

[Yarb]

The reading on the battery fully charged should be IMO 13.2-13.4 Volts. As for the electric pump scenario, the mechanical pump had been deleted by the PO? 

[SteveJ]

3 minutes ago, RJK said:

I have never given my fuel pump a close inspection, as it was on the car when I acquired it, and it never failed. I am now wondering if it may be over-spec'ed for the use. What is the best fuel pump to be running, in you folks' opinion? Should I go mechanical, or stay electrical? the cutoff switch is nice, however I have struggled with some rich running in the past, and won't be surprised if the PSI is higher than needed for 2x original SU carbs. Curious what is suggested, with an eye towards electrical since the wiring is already there. (I run mechanical on my '76 2002, and while it takes more cranking to start if it's sat for a week, it's not a problem for me ultimately).

 

@SteveJ that last pic is, for all intents and purposes, the ammeter reading with battery topped off and car running. the car came off a trickle charger yesterday, and read 12.8V before I started it today. I'll throw a DVM on it soon and get an actual number. And yes, the delta between the needle in that pic and the center line is the fuel pump draw; when i killed the fuel pump at the fuse, it was almost dead on center while running.

The discussion of the fuel pump probably deserves its own thread, but I'll go ahead and give my 2¢.

1. Measure the pressure in the fuel rail before you do anything else. It should not be more than 4 PSI. If you removed the mechanical pump, then you can measure pressure at the entrance of the fuel rail. Otherwise measure the pressure between the rail and one of the carburetors.
2. There is no fuel pressure regulator. There is only an decreased orifice at the exit of the fuel rail. If your pump outputs more than about 7 PSI, you will have too much pressure in the fuel rail. (Note: Most of the PSI ratings for the small fuel pumps are exaggerated.)
3. If you are buying a new pump, then electric is probably the way to go. I have seen too much online (and  heard from amongst Z friends) about new mechanical pumps not performing.
4. If you are determined to replace your electric fuel pump, consider a model like a Carter P4070 (https://www.amazon.com/Carter-P4070-Line-Electric-Fuel/dp/B000CIQ5DG). Keep in mind that any replacement fuel pump will require some routing of fuel lines. I also suggest considering a couple of lengths of Sidewinder fuel hose in the right diameter (https://www.amazon.com/16-Universal-Molded-Fuel-Line/dp/B07G2ZWGRG). This helps prevent kinking hoses. I used some on a friend's car, and it looked like it really belonged in the car.
5. I like having an inertia switch in the fuel pump circuit, too. It can be one salvaged from a wrecked car or a new generic one from Amazon. They can cut the fuel in an accident even if the driver is incapacitated.

[SteveJ]

Just now, Yarb said:

The reading on the battery fully charged should be IMO 13.2-13.4 Volts. As for the electric pump scenario, the mechanical pump had been deleted by the PO? 

Actually 12.8 is an acceptable voltage.

[Yarb]

That electrical pumps windings could be going bad and pulling down the system. If it’s making a ton of noise the bushings are going south as well.

[w3wilkes]

Interesting that the prior owner manually wired for an electric fuel pump. Must not have known that the stock harness from day one provisioned for an electric pump. Even Datsun dealer service used it when they came out with some of the mitigation for the vapor locking issue most prevalent in the  73 240z (ask me how I know).