Captain Obvious

And about your drain plug... M12 x 1.25 is close in both diameter and pitch to 1/2 - 20. It's either metric M12, or someone in the past stripped out the old one and retapped for 1/2 - 20.

Why do you think you're going to have a problem with the rear bearings locking up? Do you think you may have mixed up distance pieces and ended up with the wrong lengths? When I was working with Matthew, first thing we did was check his hubs and distance piece measurements to make sure he had the right pairings. Measuring the distance piece is easy, but measuring the distance between the bearing seating surfaces was a little more difficult. You can hold a block of something against one side and then measure the distance between the two faces with a depth micrometer (or using a caliper as a depth measuring device), but it's a little hokey. In the name of accuracy, I wanted a direct reading. So I donated a cheap caliper to the cause... I ground the internal reading jaws off one of my calipers so they would fit into the center of the hub and provide a direct (no interpolation) measurement between the two bearing faces. Here's the caliper with the top set of jaws ground off: And with those jaws removed, it fits down inside the hub like this:

It's easy to get yourself into a tailspin with a handful of paint samples. I think either of those would work out just fine. I suspect the original paints have all darkened a little over time, so picking the slightly lighter of the two is probably perfect.

Excellent. Glad you got it fixed! My son wanted a car and the one he wanted was derelict with significant engine troubles. I told him I would help him buy it and fix it, but he was going to do most of the work himself. I wasn't going to fix it for him, but I would help him with it. Of course, there were bumps along the way and things he realistically just did not have the experience to do himself, but in the end it worked out great. He's got a lot of sweat equity in that car and a healthy understanding of the work that he did. He doesn't baby it, but he knows that if he breaks it, he'll be the one turning the wrenches to fix it.

Awesome. Best year ever. You got questions? We got answers!

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.

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!

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

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.

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: