Weakness Revealed in the GMB and Spectra Mechanic Fuel pumps

[zKars]

Here are a couple of pics “under the hood” so to speak on the Spectra pump I’m testing.

Here is the internal divider wall between the intake and output check

and here is the cap showing its internal divider wall in line with the lower one. When I first opened it the cap was 90 deg out.

I tried putting the cap back on “wrong” this morning to see if I could get it to run for a while then quit, but no such luck. Pump output, as seen by taking a hose off the carb, was 0, nadda, szilch. Switch it back and boom, perfect working pump.

 

Edited August 18, 2020 by zKars

[zKars]

Just for grins, I checked a new equivalent Spectra pump for a 510  that I have in stock. Popped it’s cap and it’s assembled right.

I just put an electric pump in this Z, so I’m going to get the owner to run it with the fuse pulled for as long as he can stand it, and let the “fixed” mechanical run and see if it quits again. Easy to get back on the road if it does with a simple fuse insertion.

At this point, knowing this pump can run at full pressure and flowrate after having failed, the only other failure mode might be heat related where maybe the check valve flaps stop sealing well after a period of time, then re-form and work again after they cool off?? The main diaphragm is just fine, 

[SteveJ]

I took the top off of a Delphi. It is not a confirmed failed pump. It was assembled how you said it should be.

[zKars]

2 hours ago, SteveJ said:

I took the top off of a Delphi. It is not a confirmed failed pump. It was assembled how you said it should be.

Was there reason to believe it was giving problems before? Is it new?

[SteveJ]

24 minutes ago, zKars said:

Was there reason to believe it was giving problems before? Is it new?

It is new. I replaced the original factory fuel pump on another person's car with the Delphi. The car ran well at first but then had some performance issues that indicate a lack of fuel. I replaced the Delphi with another fuel pump I removed from my own car (and was operating fine when removed) a few years ago, looking to see if that was the cause. I have been eliminating one thing after another on that car, and I might actually put the Delphi back on in case the other fuel pump is a contributing issue.

At the risk of threadjacking I have already

1. Cut apart a fuel filter to look for debris. It was pristine.
2. Checked the oil in the carburetors (and replaced a piston damper that came apart when the clip at the bottom came off)
3. Adjusted the front float when I discovered there was almost no fuel in the bowl
4. Rebalanced the carburetors. (It was so far out of balance it was only running on the rear carburetor. Don't ask me how it EVER ran well like that.)

Now I plan to

1. Look for air leaks around the throttle shafts and intake manifold.
2. Monitor fuel pressure to see if it drops 
3. Inspect the banjo filters
4. Disassemble/clean the needle valves
5. Re-install the Delphi pump

Not necessarily in that order. So, I figured I would inspect the fuel pump based upon this thread before I re-install.

[Trnelson]

Here lies the culprit in my recent swap. Either the return spring is faulty or the rubber diaphragm in the check valve is faulty. I reinstalled the originals and she ran like a top

Edited August 19, 2020 by Trnelson

[zKars]

11 hours ago, Trnelson said:

Here lies the culprit in my recent swap. Either the return spring is faulty or the rubber diaphragm in the check valve is faulty. I reinstalled the originals and she ran like a top

That’s something I haven’t seen before. That’s an OEM check valve isn’t it?  If you poke the valve disk, can you get that disk to reseat or is it deformed and stuck like that?

[duffymahoney]

So I rebuilt a hand full of stock ones, I got some datsun pumps off ebay for a different model. Then swapped the guts.  Worked perfectly.  

[7tooZ]

51 minutes ago, duffymahoney said:

So I rebuilt a hand full of stock ones, I got some datsun pumps off ebay for a different model. Then swapped the guts.  Worked perfectly.  

I just did the same. Rebuilt an old Nikki with parts from a new 510 Nikki. Pretty simple after you do the first one. Had a new GMB and opened it up. The check valves looked different so didn’t use them. 

[Trnelson]

9 hours ago, zKars said:

That’s something I haven’t seen before. That’s an OEM check valve isn’t it?  If you poke the valve disk, can you get that disk to reseat or is it deformed and stuck like that?

That is the check valve from the GMB that I cannibalized, made it about 20 miles. I tried to reseat the rubber but it kept flipping back up. It gives me concern about the quality of the main rubber Diaphragm. 

[zKars]

That’s excellent feedback. Good to know that check valves are a problem too. 

\Sorry I mistook it for an OEM. I’ve never dug one out of the body. With those stamped in valves, how did you get it stay in after you removed it?

[Trnelson]

2 hours ago, zKars said:

That’s excellent feedback. Good to know that check valves are a problem too. 

\Sorry I mistook it for an OEM. I’ve never dug one out of the body. With those stamped in valves, how did you get it stay in after you removed it?

I was using the GMB as a parts donor for my KD pump. I ground out the “nubs” to get the check valves and installed them in the KD pump using the screws and plate. The sizes of both the the valves and squared o-rings were/are a perfect fit. There just seems to be aa issue with the rubber portion of the check valves. I hope they can figure it out because it’s a great way to keep the original housing with new internals.