Captain Obvious

Forgot... You mentioned in your original post that you tried mechanical pump only, electric only, and Mech+Electric combined. When you were trying the mechanical pump only, was the electric pump in the circuit at all, or was it bypassed? In other words, were you pulling through it even though it was not running, or was it completely non-existent? I'm guessing it was non-existent, and you installed it in an effort to alleviate the problem we are discussing. But I figured I would check just to be sure.

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. Just so I don't have to keep hunting for them on Airtex's crappy website, here are a few (mostly useless) documents from Airtex: http://test.showmetheparts.us/BIN/documents/Airtex/Universal_Fuel_Pump_TSB.pdf http://test.showmetheparts.us/BIN/documents/Airtex/X93273.pdf (Note that if you take a look at the "Make the final check" section of this second document, they talk about potential noise caused by a reciprocating piston). And a couple parting thoughts about the pumping capacity of that pump... They say it will do 30 gph, but they say that is the "Freel flow" (GPH (Free Flow): 30 ). I'm not sure what they mean by "free flow". I'm guessing that it either means 1) what the pump will provide if it is pumping directly into an open container like a bucket with zero head pressure to fight against. Or 2) what the pump will allow to be pulled through it if the pump is off. In any event, I agree that it is difficult to believe that an L6 could drink 1/2 gallon in a minute, but don't forget that a lot of that flow is simply going through the restriction orifice and back to the tank. The question is when you shunt that flow back to the tank, is it conceivable to believe that the L6 can drink the remainder (and want more).

Like the string and the angioplasty treatment. And yeah, I was going to tell you there wasn't any spring or ball on the stock orifice. Just an orifice. I'm no fuel pump expert, but i's clear there is a capacity issue somewhere. I hope it isn't a problem with the tank. I did a little looking into the Airtex E8251, and there are plenty of people out there who seem to think it's fine to run in series with the stock mechanical pump. 30 gph is one-half gallon per minute. How much fuel do you think you're putting through the rail in a thirty second WOT foray? And how much of that goes through the orifice and back to the tank? You could clamp off the return line and run dead headed just to see if the WOT problem goes away. Although, if you had a goober partially blocking off the stock orifice, you may have been running close to dead headed already. But the goober does bring up a question... What is the fuel pressure in the rail with the goober removed? Do you have a permanently mounted pressure gauge? PS - Out of curiosity... Anyone know what does it mean when they say that pump is "Solid State"? I'm guessing they mean the driver circuit for the solenoid pump does not contain any vacuum tubes?

Oh, and great testing BTW. I love the jar! Somewhere around here I've got pics that look just like that from a number of years ago!

I agree. If your floats are correct at idle, then setting them extra-high to account for the fuel usage at high load is just a Band-Aid and isn't addressing the root issue. And besides... All that will do is move the "time x load product" (a technical term I just made up) up a little bit. By that, I mean you will still be pulling fuel out of the bowls faster than you are putting it in, and as long as that's the case, you can eventually run them dry. I know you know this already, but what you really, really need to do is make sure your fuel supply system has enough capacity to be able to put the fuel in faster than you could possibly take it out. So let me make sure I understand your gas jar picture... You dumped the rear carb into the jar first and marked a line. Then you dumped the front carb on top of the rear and marked a higher line, right? If that's the case, then the important things to note are: 1) Good to see that the total seems to be about twice as what you got from just the rear. In theory, that means the two are about the same (as they should be). And... 2) The volumes under load are much lower than when at idle. You have sucked the bowl level down below where the venturi can pull fuel and you go way lean. So tell us some more about the fuel delivery system? What type(s) of pumps? Where are they located? And you didn't answer anything about a pressure regulator. You had previously mentioned that all three of your fuel pump combos show 3.5-6 PSI going into the rail. Do you have a fuel pressure regulator installed somewhere? If so, how about a couple pics?

LOL! Love it!

You could just plant a cherry tree in the middle of the shop. I've heard they make great anchors for dent removal and straightening. @Patcon

There is lots and lots of LED info in these threads: https://www.classiczcars.com/forums/topic/37915-sold-on-leds/ https://www.classiczcars.com/forums/topic/52446-pulse-width-modulated-pwm-dimmer-control-upgrade/

Haha! It's a LOT vague! There was a guy on zcar.com who was recently trying to adapt a pair of HIF6 carbs off an old Volvo onto his 260. He was using BCL needles. There are also recommendations out there for BCA, BCE, and BBZ. Long story short there was that he eventually gave up and went with a pair of standard HS round tops although he never really got to the root of why he couldn't the HIF's to work properly. He cut his losses and bailed. Fish or cut bait...

Yeah, those are the HIF series. Basically round tops with integral float chamber, and some other improvements. From http://sucarb.co.uk/technical-carburetter-maintenance-settings-hif: The type HIF (Horizontal Integral Float Chamber) carburetter has been designed primarily to meet the requirements of exhaust emission control carburation systems. Functionally similar to previous S.U carburetters, the HIF uses the variable choke/constant depression principle to achieve the precise induction of mixture required to control the toxic elements of exhaust emission to within statutory requirements. I wonder what needles they come with. Was that mentioned somewhere and I missed it?

Well to my untrained ear it continues to sound like high load fuel starvation. You had previously mentioned that all three of your fuel pump combos show 3.5-6 PSI going into the rail. Do you have a fuel pressure regulator installed somewhere? If so, how about a couple pics? As an alternative way to address the problem... There is an adjustable stop on the gas pedal to control how far down the pedal goes. You could run that stop up some.

Sounds like an annoying issue, and I agree with your thoughts that it sure sounds like you're sucking the bowls dry. First thing I would do is try to confirm that's what is going on. Assuming you don't have the early carbs with the bowl drain holes,... I would let the engine idle for a minute or so to make sure everything was stable. Then shut off the engine and drain each bowl into some sort of small graduated container, and measure how much fuel was in each one. Then I would make your WOT run until your O2 sensor went lean and then quickly kill the motor (coast to a stop) and then do the same fuel volume measurement again. In theory, if your fuel supply system was able to keep up under high load conditions, you should have about the same amount of fuel as when you tested it at idle. If you get very little out of the bowls, then you have at confirmed the root problem of fuel starvation. You could do the same kind of test with the clear tube "Teed" into the bowl outlet, but I'm not sure I'd want to go driving around like that . Other thoughts? I once had similar problems, and traced it to debris partially clogging the needle valve. I was running from a small engine compartment fuel source and I was frequently wiping it clean and dry with paper towels. I was not running any banjo filters either, and the fibers from the paper towels were building up at the needle valve until they created restrictions. I know you said you checked your needle valves, but thought I would throw that out there anyway. And lastly, I don't think it has anything to do with a washer under the suction piston spring.

Yeah, with the tach dropping off like that, it's probable there is something wrong on the primary side of the ignition system. And with the input from the other guys, it sounds like the ignition module is suspect.

Arrgh.

Funky! I'm sure the old-time carb guys would recognize that in an instant, but that's the first time I've ever seen something like that. Makes me wonder what was going on and caused that phenomenon. It's so even that it almost seems a relic of the original construction method. Stress risers caused by the ring rolling process to form it into a cylinder? Gear driven, and the pitch of the gears has something to do with the distance between the cracks? Hermetically sealed container that has been flexing and changing shape with many years of temperature changes and finally gave out? Some sort of corrosion phenomenon? Funky!

I was recently involved in the replacement of rear wheel bearings for two Z's: https://www.classiczcars.com/forums/topic/60026-friends-over-for-a-party-in-the-shop-yesterday/ One of the hubs had a similar issue to yours, and we (believe we) traced the problem to a bearing that was pressed in at an angle. It seemed that the bearing (mostly) eventually leveled out and went in, but not before it raised a huge burr inside the hub. And that burr prevented the bearing from seating in it's proper location. Sounds like you may have had a similar issue. Here's a pic of what happens when you try to press a bearing in at an angle. You can see the semi-circular mark on the far side where they gouged the cylinder wall that is supposed to locate the bearing. That raised bump was pushing the bearing to one side and not letting it seat square. I used a hand file to dress the high spots back level:

Keep up the good work. Don't forget to hook up the condensate drain. (The black nipple to the left of the vacuum control switch). Also, (if you haven't already) would be a really good idea to make sure the heater core and temperature control water cokk are in good shape before you put the dash in. You can get to that stuff after the dash is in, but it sure is a lottttttttttt easier with it out.

Yeah, I don't see a video either. Something went wrong there. But your comment about the tach brings up an important piece of info... The early version of the tach ran the ignition primary side through the tach, and because of this, if there are problems on the primary side of the ignition, it often affects the tach operation. So the question is... What does your tach do when your engine cuts out? Does it drop to zero? (That question is probably answered by your video?)

My pleasure. And if you find yourself down this way, get in touch and we'll see if we can pinpoint the exact problem together. And... Don't get lulled into a sense of confidence about the problem that only occurred once in a certain day. These sort of things typically only get worse over time, and one day it's likely to cut out and not come back. And at that time you will be in the most inconvenient situation and location. Better to have a handle on the problem on your schedule.

Bursts of complete cutting out does sound like an electrical issue, but it sounds like something on the primary side of the coil and not something on the high voltage side. Of course, I reserve the right to be completely off base, but I'd concentrate your efforts on the primary side. Especially if there have been known issues with the Mallory module. Good luck with the investigation. Is there an old-school points distributor you can throw in there to see what happens? Another idea would be to carry a can of freeze spray and hit the module with a quick blast next time the problem occurs.

Replacing the cap and rotor (or any other tune-up style work) with new certainly can't hurt, but I worry your sanding of the electrodes and having the problem go away is a red herring. How do you know it was misfiring? What I consider a misfire is usually harder to detect at higher RPM's. Did it cut out completely for a short period of time while you were on the highway? Or did it feel like it was just running unevenly and "pulsing"? "Judder-ing" (Is that even a word?)

That usually doesn't work out for me. I do try though!

Just because it's magnetic, doesn't mean it isn't stainless. Some stainless is magnetic, and some is not. I don't remember the grade numbers offhand, but I suspect it comes down to cost and workability. The magnetic grades are easier to work with and probably cheaper. But the non-magnetic grades usually have better corrosion resistance. Some of them work harden just by looking at them wrong though and are a pain to form.

It's really hard to evaluate using a recorded media like that, but I don't like the sound of it either. The frequency is too high. I can deal with a "tap" at idle, but it's almost a "buzz". I'm thinking alternator bearings or brushes? Or, it could just be impossible to tell from a recording like that.

Those clever suspension design guys have that covered... Non-problem. It doesn't matter. Note the bulged up (or down, depending on which side you consider "up") area where the end link contacts the control arm. It's almost an ellipse? Note that area is actually in the centerline of the control arm. When you flip it over, since it's on center, the distance is the same regardless of which side is up. Not sure if makes sense with just words. If not, I can post a pic or something to help explain?