SU carbs will not sustain Heavy load

[MY1PATH]

I checked, fuel can flow one way trough the pump when it is off.

I only drove the car once the electric pump in line but not powered (was chasing wires) and the was no noticeable decrease in performance. Before that it was exclusively mechanical and after that if it was inline it was powered. I also just remembered that when I added the pump I had to tighten my connection to the chassis hard line right after the pump...it was leaking pretty good with the pump powered.... Maybe another indicator...

 

[MY1PATH]

Lucky me, I had time to fish out the fuel hardlines. Unlucky me, both were clean. The only thing I found was little waxy gobb which probably came from the very string I was dragging through the hard line.
I think I have discovered some blockage in the vapor line, air running through it sounds muffled and my string has not been able to blow all the way through it yet. Once get it sorted I will put all the hoses back on and continue driving it. But now I have motivation to clean my garage (yay) because my next step is to drop the tank...

 

8 hours ago, Captain Obvious said:

Couple observations... First off, Airtex's website sucks. Bad.

Other thoughts?

You have suggested a couple times that the pump is a diaphragm type. I haven't seen any pics of the insides of that Airtex pump, but Airtex says it is a "Type: Solenoid" (not diaphragm). From that suggestion, I suspect it is a reciprocating piston where the piston is magnetically driven (solenoid). That is how the original 240/260 pump worked, and (based on the description and mechanical shape) I suspect the Airtex is the same. I do not believe there are any diaphragms inside that assembly.

The reference to "solid state" exists in a number of places on-line, but curiously enough, not as part of Airtex's own description of the pump. So it seems that part of the description was either made up by someone other than Airtex, or it used to be called that by Airtex some time in the past, but is not anymore.

Knowing I was shooting for 3.5-5 psi for an electric pump without needing a regulator; I bought this pump based off recommendations and reviews. Some reviews were from other Z owners, its same-spec sister that comes with a filter was found on another thread but I like the larger off the shelf clear filters for the 260z so I bought the filterless model instead. I find more and more that the info provided by manufacturers (or re-labelers) has become increasingly lacking over the years...

This is where I saw "solid state" https://www.amazon.com/Airtex-E8251-Universal-Electric-Applications/dp/B0027I88VQ
My mistake on calling it diaphragm however, the principle of an electromagnetic coil moving a pin on a diaphragm or a piston on a solenoid is still the same even if the moving parts themselves are different. 

 

Edited June 1, 2018 by MY1PATH
Pic via Mobile, Txt via PC

[Captain Obvious]

Nice. What's the gray goober? Looks like silicone sealant, but it shouldn't be inside the tubes.

I don't have any silver bullet as a fix for the problem, but at least in theory, the problem has been identified.

You said that before you installed the electric pump, it was exclusively mechanical. Did your WOT lean problem occur in that configuration? Is that why you started messing around with adding the electric pump?

You can try a dead headed WOT run with the return line to the clamped shut just to see what happens.

You can run a capacity test on your electric pump up at the rail by disconnecting one of the lines to a carb. You probably won't get the half gallon in a minute because some of that will be going back through the orifice to the tank. The mechanical fuel pump will also eat up some of the pressure due to the cracking pressure of the check valves built into the pump.

You could bypass the mechanical pump with a piece of tubing just to see what happens.

Just tossing out some investigative ideas before you pull the tank.

[Captain Obvious]

Well here's to hoping you don't have to drop the tank. Good luck and I hope you find the root problem!     

[MY1PATH]

7 minutes ago, Captain Obvious said:

Nice. What's the gray goober? Looks like silicone sealant, but it shouldn't be inside the tubes.

I don't have any silver bullet as a fix for the problem, but at least in theory, the problem has been identified.

You said that before you installed the electric pump, it was exclusively mechanical. Did your WOT lean problem occur in that configuration? Is that why you started messing around with adding the electric pump?

You can try a dead headed WOT run with the return line to the clamped shut just to see what happens.

You can run a capacity test on your electric pump up at the rail by disconnecting one of the lines to a carb. You probably won't get the half gallon in a minute because some of that will be going back through the orifice to the tank. The mechanical fuel pump will also eat up some of the pressure due to the cracking pressure of the check valves built into the pump.

You could bypass the mechanical pump with a piece of tubing just to see what happens.

Just tossing out some investigative ideas before you pull the tank.

The electric pump was purchased for a few reasons:

-aid in starting after sitting (done)

-to hopefully replace the mech pump (done, mech pump has been sitting in my garage ever since I concluded the car can run fine without it)

-solve the sustained load leaning out (wishful thinking and nope)

I have been driving with this problem running exclusively on a mech pump for years but often other things take priority. The car is still fast enough to get me into trouble before starving out and the top of 1st gear is speeding anywhere on my daily commute (3.55:1 gears).

My buddy said he had the same problem once... It was a hole in the in-tank pickup above the fuel level, it would pump fuel but not as optimally as it could due to the loss of suction through the hole...

I'm gonna bit the bullet, clean the garage and hopefully have time to drop the tank sometime soon...

[Captain Obvious]

Well good luck, and make sure you tell us what you find!

I've got some pics around here somewhere showing the internal guts of the original electric pump. No diaphragms anywhere. None. Two ball-spring check valves. One stationary on the inlet, and a moving one on a magnetically driven plunger. Plunger moves up, pulls fuel in the inlet check valve. Plunger moves down (closing the inlet check valve) and pushes that fuel out through the check valve mounted in the center of the hollow plunger/piston. Reciprocates up and down pulsing fuel out.

Sort of a seal around the reciprocating piston simply because it's a precision fit inside the tube cylinder of the pump. Tight enough to mostly seal, yet loose enough that the piston has clearance to slide up and down.

I have no idea if that is a similar construction to what's inside the new Airtex, but if I find the pics, I'll post some of them up. Very simple, and no bendy diaphragm to wear out. Fun to look at if nothing else! 

[MY1PATH]

1 hour ago, Captain Obvious said:

Sort of a seal around the reciprocating piston simply because it's a precision fit inside the tube cylinder of the pump. Tight enough to mostly seal, yet loose enough that the piston has clearance to slide up and down.

I have no idea if that is a similar construction to what's inside the new Airtex, but if I find the pics, I'll post some of them up. Very simple, and no bendy diaphragm to wear out. Fun to look at if nothing else! 

Sounds good for longevity as long as it doesn't bind. My Z had the factory pump when I got it. It made noise but didn't move fuel so I threw it away and went exclusively mechanical on the L26. Sustained load issues didn't come up until the L28 went in, it was probably right on the edge before the swap.

[Captain Obvious]

Thinking about it a little more, the method I suggested earlier on how to run a capacity test as described above won't provide information that really matters. Reason being, if you pull one of the hoses that lead to one of the carbs, you have changed the head pressure against the pump. The needle valves are a significant restriction and what you really need to see is how much fuel you push through one or both of them. In other words, what you REALLY need to see is how much fuel gets to the bowls. And with that in mind...

You could pull off one (or both) of the tubes between the bowl(s) and carb body(s) and run your fuel pump for a minute and see what you get out. It would probably be significantly less than what you would get if you would check at the rail before the needle valves because the fuel will be split between getting pushed through the needle valve(s) and getting pushed back into the tank through the orifice.

Just because you've got strong looking flow at the rail running into an open container doesn't necessarily mean you've got adequate flow into the bowls while in use. It's clear from the existence of the problem that the amount of fuel being pushed into the bowls "in use" isn't enough. It would be interesting (to me anyway) to see how much fuel that really is.

There would still be a little error using that method because of the amount the needle valve is opening, but it should give you an idea of the max amount that COULD get into the bowls if the floats were completely hanging and the valves were as open as they could possibly be.

[Patcon]

If you do drop the tank, try to get your hands on a flexible camera scope. It sounds like you might have access to one of those. It will make checking the tank easier. The other option is cutting it open, which would be my last resort. You should have access to the pick up lines from the fuel level sender hole, but I believe there is a tank baffle that blocks a direct view of them

[MY1PATH]

So I finally got a string through the chassis vapor hard line. The other lines only took 40 PSI and blew string through quick and easy, they also pulled without too much difficulty. This vapor line took 120 psi and several minutes of air blowing without feeding and then it would take up a few inches and stall again... Granted its smaller and has a few more bends in it than the fuel hardlines but my string does not want to move without a lot of resistance (let alone drag a mop through it to clean it out) 
Is it possible that the cause of my problem was tank vacuum limiting my pump?  
I would test this theory by driving without the gas cap but I'm determined to get this string pulled all the way out of my vapor line before put wheel back on and get the car back on the ground...

Edited June 2, 2018 by MY1PATH

[grannyknot]

6 hours ago, MY1PATH said:

but my string does not want to move without a lot of resistance (let alone drag a mop through it to clean it out) 

You could try a length of thin gauge aircraft cable, stiff enough to be able to push on but flexible enough to go around the corners, it may also clean out some of the accumulated crud.

[240260280]

Vapour line does little.  You seem to be running out of fuel in the bowls or have some sort of strange air leak into the manifold that increases with rpms.