1405 lean at WOT

Fuel and Air Systems

  1. 67cuda318

    67cuda318 Member

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    Hey all. New here, and pulling my hair out over this carb.

    Some specs:
    318, with an eddy 1405
    live at 4200', so it should be jetted at least 4% lean.
    FPR set to 4psi.

    I've had this carb for about a decade since I last rebuilt it. It was running alright, but I wanted to lean it out a bit at cruise. I have an LM-1 wideband to tune with.

    I changed a few things, and got it leaner at cruise. But at WOT, it was too lean (mid 13s), and didn't seem to pull like it should. I forgot what jets I had installed, so I opened it up, and the secondaries are .101"s. aka, 8% richer than baseline. It should have been really rich given my altitude. I had planned to go one step bigger, but they were already huge :eek:

    To know exactly where I was, I went back to #22 on the 1405 chart, with the secondaries at baseline (0.095"), and it was rich at cruise and power (mid 12s), and 13.5-14 at wot :wtf:

    Opened it up again tonight, and the bolts holding the secondary venturies weren't super tight. Cleaned everything, checked the floats, went to #24 on the chart, put it back together, and now WOT is even leaner, around 15. Cruise/power went a tiny bit leaner, but not much.

    Any ideas why I'm so lean at wide open throttle?

    :thankyou:
    https://edelbrock-instructions-v1.s3.amazonaws.com/edelbrock/carb-tuning-guide.pdf
     
  2. Aaron65

    Aaron65 Well-Known Member

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    It looks like you should be aiming for the lower right quadrant of the tuning graph, not the lower left; my experience with Edelbrocks is that changing the secondary jets is for fine tuning. It looks like you may want to study #23 and #26 on the graph; they SHOULD lean out cruise and richen up the power circuit. By going to #24, you leaned out the power circuit. Also remember that you shouldn't be aiming for a specific number on your wideband; give the engine what it wants. All engines are different; use the wideband to make sure you're in the ballpark. Obviously, you're a little out of the ballpark right now, but you'll get there.
     
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    • fklskv

      fklskv Well-Known Member

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      :steering:So it ran good for ten years and then you decided to fix it?!
       
      Last edited: Apr 3, 2021
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      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        Excellent and concise.
        :thumbsup:

        Example of fuel mix at WOT top gear where readings of 13:1 developed more power than 12:1 in this post.
         
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        • 67cuda318

          67cuda318 Member

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          Awesome :thankyou:

          So the primary (ha) source of fuel at wot is the power circuit, with the rods up. That makes sense that when I went to #24, wot got a little leaner.

          At one point in my testing I ended up at #15 on the 1406 chart (which gave 14ish afr at cruise). Going right to #17, it's really close to #26 (on 1405). I may try #18 (1406) since I have those rods & jets already, and don't have the rods for 23 or 26 (yet).

          I'm a glutton for punishment :BangHead: It's been that long since the rebuild, but I changed several other things along the way (electronic ignition, timing curve). I wanted to lean out the cruise a little, and the wot got worse. Huh? :realcrazy: Now I know why.
           
        • Bewy

          Bewy Well-Known Member

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          Just something to be aware of with Edel AFBs.....
          I have heard of the 750s having the emulsion tubes restricted in the secondaries. Not sure about smaller cfm models, but should be checked. You might want to remove the sec boosters/venturiis & check. Unlike brand H & clones, you won't need any gaskets if you are careful.....
          After removing the venturiis, look at the large brass tube hanging out the bottom. If it has a bullet shaped end, it probably has the dreaded small 0.073" hole in it. This small hole feeds that barrel & gets fuel from the sec m/jet. Obviously, if the sec m/jet is say 0.089", the 073 hole controls the flow, not the larger m/jet......as designed. Carb runs lean & nothing seems to fix it....
          The fix is to cut off the bullet shaped end. If there is NOT a bullet shaped tip, all is good & nothing needs to be done. Button it up.

          Another possible reason for running lean at WOT is a bad fuel pump, either low pressure or delivery or both.

          Why Edel did the above is beyond comprehension...............
           
        • threewood

          threewood Well-Known Member

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          Are you verifying afr with a dedicated wideband o2 sensor or a tailpipe clamp on sensor?
          Verified fuel pressure at wot?
          Are you getting a lean stumble/pop at wot?
          Mechanical or electric pump?
           
        • 67cuda318

          67cuda318 Member

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          Bewy, The large tube in the secondary boosters don't appear to have a restriction like that.

          Dedicated wideband O2 just past the collector (dual exhaust, with no crossover)
          No easy way to verify fuel pressure at wot.
          No pops or stumbles at wot
          Mechanical pump
           
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          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            Dont worry about that stuff unless something comes up that points that way.
            Focus on what Aaron posted.
             
          • 67cuda318

            67cuda318 Member

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            I went to #18 on the 1406 chart (pretty much right between #23 and #26 on the 1405 chart). It's still in the mid 12s at cruise and rods up, and 13-14 at wot?

            It pulls really hard though :D

            When I get more time I'll go back to my previous tune, and make smaller adjustments from there.
             
          • Slantsix64

            Slantsix64 Well-Known Member

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            i thought edelbrocks like 6.5 psi not 4.0?
             
          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            It's not a matter of like or dislike. It is easier to maintain a full bowl with lower inlet pressure. It depends a bit on the how the regulation is down, the amount of restriction in the inlet and pump flow relation to pressure. 6.5 psi is about the upper limit what the inlet - float system can handle.

            If you want an example of how this works both in theory and in practice, Cudafever tested it out with his electric pump on his race car.
            Holley/Demon Carb stumble
             
          • 67cuda318

            67cuda318 Member

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            Took another short drive today, still at #18.

            At cruise, rods down, it's 12.5 to 13.5
            part throttle, rods up, it's 10 to 10.5
            wot is still 11-13

            If I lean out the part throttle, I think it's still going to make wot go even leaner, right?
             
          • Bewy

            Bewy Well-Known Member

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            Float level & fuel pressure. Because of the excellent leverage system on Carter/Edel 4 bbl carbs [ AFB, AVS, TQ ] they will accept a LOT of fuel pressure & not flood. I have run 12 psi at the track chasing a lean problem on a TQ, no hint of flooding. It is a non-issue.
            Fuel pressure & n/s size affect the final fuel level in the bowl. Higher fuel pressure & larger n/s size will raise the fuel level [ & vice versa ], so the float adjustment # should be increased to compensate. Carter published a chart showing the changes reqd.
             
          • Aaron65

            Aaron65 Well-Known Member

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            It's tough to tell you what to do because those numbers are all over the place. Your cruise is still a little rich, but 13.5 isn't too far off the mark. Under hard acceleration, you have to let the accelerator pump shot "clear out" before you get a reliable number; in your case 11-13 is quite rich to just about right (that's a huge spread). For full throttle testing, it might be a good idea to record the gauge with your phone so you can keep an eye on your driving and get a steadier number. Part throttle is rich, but the accelerator pump shot will make your reading look rich for a second or two, so make sure you're pushing the pedal slowly to get a more accurate reading.

            Your numbers will vary as you drive based on acceleration, deceleration, hills, etc., but if you hold the car at a steady 70 mph or so, that number will be your cruise, because you are now operating on the mains and not the idle/transition circuit. Remember that cruise and power work on different parts of the metering rod, so richening or leaning out cruise will have little to no effect on power, and vice versa.
             
          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            One more thing. Cruise at 35 mph is very different than cruise at 65 mph.
            The difference is mostly the load at 65 is higher, this requires more throttle opening and is the place to judge if the primary main circuit is too lean. When its too lean, you'll know it! Just back off the throttle and drive slower until you an get to a safe place to change the rod/jet combo. wink-gif.gif
            Assuming the off-idle was close, the transition will then be pretty close.

            Next thing to fine tune if you want is the enrichment point. This one is not easy. Use a video or a friend to help. Power should increase with increasing throttle (and corresponding drop in vacuum). If there is a dead of flat spot, or if the power suddenly increases with the step up raising the rods, then the step up point needs to be adjusted. For increasing power, AFR should be going leaner with increased throttle opening - until it needs to go richer. That's what the step up rods do.

            See illustration here Power Valve Selection: The Definitive Answer
             
          • 67cuda318

            67cuda318 Member

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            I think I was making too big of changes, so I went (almost) back to my last known good tune:
            095" primary
            104" secondary (this is increased from a 101" I had in the past.
            68x42 rods, silver springs

            The vacuum readings here are 1-2" lower than what my analog gauge shows.

            In this image, the first callout at 4:25 is moderate acceleration. At 4:35 I ease off a little, and the vacuum rises, and the rods go down, and afr leans out a bit. At 5:07, after coasting a bit, I go to WOT starting at ~50mph). It goes way lean, then stays pretty lean.
            Screenshot 2021-04-10 210839.png

            In this one, I go to wot from about 30mph. It spikes rich, then stays over 14 afr for the run.
            WOT.png

            I don't think I want to go richer on the power circuit. The wot readings just shouldn't be that much leaner, should they?
             
          • Aaron65

            Aaron65 Well-Known Member

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            OK, your current tune is way off on the lean side of the chart again (#27), so it makes sense that WOT should be lean. I think the reason you're seeing rich part throttle acceleration is because you have silver step up springs in there, which are the strongest step up springs. I've never needed anything stronger than the pink (7") springs, and I usually use the orange (5") spring. You might be hitting the power stage before you need it.
             
          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            I agree the WOT is lean, but since its in 1st gear it's not likely at maximum loading. It's somewhat common for WBO2 to indicate a higher AFR at WOT in the lower gears than in top gears. It depends on the combination. But regardless, 14:1 is too lean.

            Get the WOT full load mixture where it will make best power. This requires a dyno or 1/4 mile run. That's the jets.
            Lean the cruising at 65-70 mph afr as much as it will tolerate. Make it a hair richer if your not sure. That's the jet and rod size combo.
            Then if you want you can experiment with the step up springs. Factory Chrysler engines were relatively efficient. It shouldn't need to enrich until something around 8.5"Hg or even a little lower. If the engine has been hot rodded or intake manifold change, then it might need enrichment as early at 10.5"Hg. See the post linked above about 'power valve tuning' and the second log in this post showing crowding vacuum.

            I've found the same. I don't know its in the nature of the vacuum system or how the MAP works. With Logworks the table can be adjusted. In general I just live with it. Since you drive in a location with very different air density (eg high altititude) the table can be, and probably should be adjusted to start the vacuum reading from the actual local atmospheric pressure. Depending on the particular logger setup, its may be possible to have the MAP sense the local absolute pressure and then with the engine running provide vacuum reading derived from the actual difference. Is this an LM1 with a LMA-3 Auxbox?

            upload_2021-4-11_9-24-37.png
            There will be a pump shot down spike at any accelleration beginning from a low throttle position.
            The pump shot is fine for now. You can come back to that later if you want to attempt finer tuning.

            When the throttles are closed or slightly open, the fuel is supplied by the 'idle circuit'. The 'idle circuit' delivers most of the fuel when cruising at less than Interstate speed. It doesn't take much power to keep a keep moving steady on flat roads.
             
            Last edited: Apr 11, 2021 at 8:51 AM
          • 67cuda318

            67cuda318 Member

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            I think that makes sense. What set this whole thing off was chasing an off-idle stumble. Going from Orange to silver seemed to cure that. And while I'm at it, why don't I lean out the cruise just a little bit more... wait, what is wot doing???

            I have the LMA-2 RPM converter. I found an MPX5100DP pressure sensor I had laying around, and used a 7805 voltage regulator to power it (along with a couple decoupling caps). I entered two points in logworks according to the curve in the datasheet. I'd assume that's more accurate than the analog gauge, but at least they're close. I have rpm hooked up, but for some reason it's not being read correctly.


            I'm just not sure how I can richen up wot much, other than different jets and rods to get more fuel in power mode. But doing that makes it really rich during acceleration when I'm not into the secondaries yet. I already have the biggest jet I have in the secondaries (.104).

            Side note: A while back I found an excel file "tunabrock" that lists every combination of jets and rods, and their resulting area for fuel. Makes it easy to compare different rod/jet combos. I was just making too big of jumps :rolleyes:
             
          • Aaron65

            Aaron65 Well-Known Member

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            An off-idle stumble won't be cured by the step up spring unless it's a WOT (or heavy throttle, at least) off-the-line stumble. A light throttle stumble is a lean idle circuit, which is outside the scope of what we're talking about here. If it were my car, I'd go back to the orange spring and get your jetting closer to the #23 and #26 we talked about above and see how it works. If you then have an off-idle stumble, we can talk about it then.
             
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            • 67cuda318

              67cuda318 Member

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              It was a fairly heavy throttle stumble. My driveway enters the highway from a slope, so I need to hit it fairly hard. It's not a casual start from a stop light on flat ground.

              I'll look at getting a 70x37 set of rods, for #26.

              Though looking at the spreadsheet, #23 and #26 have the exact same power area, and the cruise area is virtually the same (0.00367 in^2, vs 0.00369 in^2). (For comparison, from #21 to 24, goes from 0.00369 to 0.00336, much bigger change for 1 stage difference. Oh, look at those weeds over there...:poke:).

              :thankyou:
               
            • Mattax

              Mattax Just the facts, ma'am FABO Gold Member

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              That's what we're asking! LOL.
              upload_2021-4-11_13-23-0.png
              A. Rod jet combo 2, 3, 23, or 26 will get much richer WOT on the primaries.
              I'd start with 2, then try 23 or 26.

              B. The guiding method here is one change at a time. Leave the secondary jetting where it is or return it to the baseline and leave it there for now. Heck, I'd rig them so they couldn't open but that may be more than you're willing to do.

              By going to Combination 2, that is supposed to only change the WOT AFR. Then going to 26 will let you experiment with whether it will tolerate a leaner high speed cruise. Keep working on it step wise. Too lean at cruise the engine will rev and try to die. That's too lean. Test this in location you can safely drive back at slower speed, like 55 mph.

              I erased the description low power because its not quite correct and may be misleading.
              As the throttle is opened, the engine darn well better produce more power. And if its not a complete dog, it will make the most part throttle power with leaner mixtures. Leaner than cruise.
              Nearing WOT and maximum load, the engine needs to get a much richer mixture.
              If there's no load, the engine can run quite lean. You can wing the throttle wide open with the tranmission in neutral and it will rev to 5000 at 16;1 - no problem at all. Well maybe the engine won't like being free revved like that but that's another story. LOL

              H'm. Interesting. Wonder why LM-1 is showing in the logworks screen shot.
              Because I'm using the Auxbox for rpm I haven't made up a cable to try out the LM2 rpm input.
              Since you're successfully using the pressure sensor, I would like to think that the other input functions are working. You may have to keep experimenting with the input signal or the table to get the rpm or frequency to function.

              For the MAP, one procedure I usually add in the routine is to record a session about 20 seconds when the engine is shut off. it takes a couple of seconds for the MAP to show atmospheric pressure. That provides a reference for 0"Hg Vacuum.
               
            • Bewy

              Bewy Well-Known Member

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              Put the A/F meter away.....
              Step up rod springs. To select the correct ones for THIS engine:
              Start with the strongest set. Loosen the piston cover screw 2 turns, enough so that you can swivel the cover such that you can see the piston but it is still captured. Lock the screws in this position. Warm up the engine, put in gear if auto. If springs are moving AT IDLE, they are too strong. Change to next strongest pair etc, UNTIL pistons do not move at idle. Those are then the correct springs.
               
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