Jump to content

MY1PATH

SU carbs will not sustain Heavy load

Recommended Posts

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...

KIMG0450~2.JPG
 

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 by MY1PATH
Pic via Mobile, Txt via PC

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites
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...

Share this post


Link to post
Share on other sites

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!  LOL

Share this post


Link to post
Share on other sites
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!  LOL

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.

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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 by MY1PATH

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites

Does anybody know what size the small hole in the float needle valve is supposed to be?
Maybe I got the wrong one? Or maybe folks on performance builds are running a larger size?
I've seen them go all the way up to 0.125" on other SU's for other engines (race builds)
 

12 hours ago, grannyknot said:

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.

I got it out. Much shimmying in each direction with compressed air helping each direction. Something came out of the vapor line, I just didn't see it but the string was able to slide freely and drag a mop through when I was done.

8 hours ago, 240260280 said:

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.

Not an air leak, the problem does not come with RPM, it comes with sustained load and we've already proven the the carbs are running out of fuel when this happens.

Share this post


Link to post
Share on other sites

I'm not sure there is a "standard" size for the needle valve hole. I wouldn't be surprised if different manufacturers might have different sized holes there. What's the hole size in yours? I've got a couple around here that I can compare when I get the chance. Are your valves original, or aftermarket?

And as for the vapor line potentially causing the problem, I doubt it, but it certainly wouldn't hurt to check. I was going to suggest a run with the gas cap off or loose, but I really don't see it. And even if there is a problem with the venting, it's not caused by the vapor line. The gas cap itself is supposed to have a check valve built into it such that it allows air into the tank to replace the volume of fuel removed.

If that valve in the gas cap is blocked and doesn't work, you could draw a vacuum on the tank and make it hard to pull fuel out. Although, I'm not sure you would see that stark of a difference between WOT and just cruising around normally. Nor would I expect it to be that fast acting or repeatable.

Share this post


Link to post
Share on other sites
1 hour ago, Captain Obvious said:

I'm not sure there is a "standard" size for the needle valve hole. I wouldn't be surprised if different manufacturers might have different sized holes there. What's the hole size in yours? I've got a couple around here that I can compare when I get the chance. Are your valves original, or aftermarket?

Mine are aftermarket. I can't remember where I got them from but it was a kit with lid gaskets, needle valves and hoses (I used Tygon hose instead). Tomorrow I will take them out and measure them (forgot to today).
From looking around I think S30's and other small HS carbs got .070" from Skinner Union but I might try to order some .096" ones...

Edited by MY1PATH

Share this post


Link to post
Share on other sites

I will start digging around here to see what I have. Of course, I have no idea if what I have is factory or aftermarket. And I've also got a number of float valves from flat tops... I wonder if they are the same. I never looked into that.

I would be really surprised to find out that the difference going from a L24 to an L28 is enough of a change to push you over an edge like that though. I guess I've seen stranger things, but it would just be surprising. Makes me still wonder if there's something wrong with the delivery system somewhere upstream of the needle valves.

Finding needle valves with a larger through hole might fix the symptom, but still might not be reversing the root problem, just accommodating it. Although, if that's the case... does it really matter? Fixed is fixed?     :)

Share this post


Link to post
Share on other sites

 

2 hours ago, 240260280 said:

240z needle valve is 2.0mm (below).

I can not find data for 260z.

Thanks! This is exactly what I need, 2.0mm/0.0787"

3 hours ago, Captain Obvious said:

I will start digging around here to see what I have. Of course, I have no idea if what I have is factory or aftermarket. And I've also got a number of float valves from flat tops... I wonder if they are the same. I never looked into that.

I would be really surprised to find out that the difference going from a L24 to an L28 is enough of a change to push you over an edge like that though. I guess I've seen stranger things, but it would just be surprising. Makes me still wonder if there's something wrong with the delivery system somewhere upstream of the needle valves.

Finding needle valves with a larger through hole might fix the symptom, but still might not be reversing the root problem, just accommodating it. Although, if that's the case... does it really matter? Fixed is fixed?     :)

I totally forgot I had a set of Flat Tops... If the valves are similar I might try them or even try to ream them out without worry of ruining a good set. Better yet I wish I knew where my original valves were as well as the new spares (kits came with one long and one short for each carb)
To some extent it may matter... IF The problem is fixed stopped one way but if the root cause worsens does the problem come back?
Needle & Seat Kit. Steel 0.156" - H8 Carburettor
Just for fun: High Flow 0.156" Needle Valve for SU H8 used on 3.4L Jaguar straight 6...
 

 

Edited by MY1PATH
numbers

Share this post


Link to post
Share on other sites

At a glance Flat Top valves are nothing close so I stopped right there.
Just measured my round top valves at #52 or 0.0635" (1.61mm, side is stamped "1.7" which is only .0025" difference)
That's over .0152" (0.39mm) too small. If I was within 0.010" I would not be so concerned but I would rather be bigger than smaller.
The more I think about it, this actually MAKES A LOT OF SENSE!!! L28 and carb rebuild happened at the same time... 
On the L26 I took the carbs right off Ebay, installed them and they ran ok so that was that... When I got ready to install the L28 I took the carbs off and rebuilt them, to include viton O-rings on the shafts (I think I copied someone Obvious) and of course the new Needle Valves. If I can find my old parts I will measure them too I think they were original.

The Viton Tip is just under 0.150" (not going quite that big) so if I find my spare set will will see if I can successfully ream and debur them without having them leak afterwards.
If I can't find spares new ones are going to be $30+ per carb and I'll have extra viton needles too, just don't lose them this time lol.

Edited by MY1PATH

Share this post


Link to post
Share on other sites
9 minutes ago, Stanley said:

Still using stock N-27's ?

I actually don't know what needles I have, there are no visible markings but I suspect they are N54? I read somewhere that those are really Fat idle and lean up top.
I think the SU's came of 1972.
I have some damaged needles out of a flat top that I have heard are the opposite, I might try to clone those...

Edited by MY1PATH

Share this post


Link to post
Share on other sites

I found one round top needle valve. I have no idea if it's factory or aftermarket, but it is the old style with the hardened steel seat and the regulating spring built into it.

It measures .079 through hole, so it's at least what the book says is correct.

I'm pretty sure I've got a couple others around here somewhere, but I don't know when they will turn up. I will keep an eye open for them though and let you know if something turns up.

Share this post


Link to post
Share on other sites

Sorry for the silence, I have opened up the flow buy reaming the needle valve seats to 0.0995" and adding side exit ports. This helped the problem but it did not completely eliminate it. (Power cuts out more softly and recovers quicker)
Solving this problem has slipped back down on the priority list a few notches but my next steps will be to try deadheading and then pull the fuel tank...
Got a lot on my plate right now and other things to catch up on but I will revisit this thread when I get back to troubleshooting.
35884802_2042995692440343_32826962680060

Share this post


Link to post
Share on other sites
25 minutes ago, 240260280 said:

FYI  I am rebuilding round top SU's with Hitachi needle valves stamped 2.0.   I guess they are not original size but the carbs did seem untouched. 

According to your earlier post 2.0 IS original. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.