Help me fix lean on power issue - Holley 4150

Fuel and Air Systems

  1. wsutard

    wsutard Well-Known Member

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    What about doing the opposite? Set my jets so that it cruises at the right AF but then drill out my PVCRs to allow for more fuel on acceleration (low vacuum)?
     
  2. 68 HEMI GTS

    68 HEMI GTS Well-Known Member

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    Your thinking is off, under normal cruise you’re running down the road on the transfer slots not the jets. That’s why it’s still pig rich at cruise with the 72’s. Then when you activate the main circuit it’s going lean because you don’t have enough jet. This is my car going down the road with a 1050 Dominator. The jets have little to no effect at this rpm under steady low load cruise. These carbs are notoriously fat out of the box. Careful attention to proper air bleeds and restrictions and it goes down the road like fuel injection.



     
    Last edited: Aug 27, 2019
  3. wsutard

    wsutard Well-Known Member

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    FYI, The 72s are rich because I bumped up the float level. Prior to doing so they were a nice cruise of 12-13.

    However, I see your point. You’re logic seems sound since as soon as I get into the main jets I’m seeing af immediately get lean.

    So, based on your logic, I need to size my jets for proper af under acceleration first. Second, I need to adjust the transfer slot to reduce fuel flowing through that circuit by reducing the orifice size you point out in your pics?

    Is there an aftermarket metering block that already has adjustable transfer slot orifices?
     
  4. 68 HEMI GTS

    68 HEMI GTS Well-Known Member

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    No, size the jets for steady state at high speeds where the circuit is on. Then tune the PVCR, for high load acceleration.

    you can put an aftermarket block in it or drill and tap yours. The TSR has to be in the main body. The IFR is in the metering block. The restriction for the transferslot is something you have to experiment with. Low .070’s to start
     
    Last edited: Aug 27, 2019
  5. 68 HEMI GTS

    68 HEMI GTS Well-Known Member

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  6. beanhead

    beanhead Well-Known Member

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    Yeah that float level is too high..not the answer.
    Absolutely on the timing! Not having that correct throws eeeeverything off..

    -Advance your distributor, until the RPM and/or vacuum start to peak and level off. Then you can back it off a couple degrees if desired. You'll have to (most likely) drop your idle speed screws some, which will be good for getting your transfer slots covered...looks like a total do-over but don't sweat it, 68 knows his sheeat with carbs. Once the timing's dialed, t-lots good and jets corrected you may not even need to get tooo crazy with the drill:)
     
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    • beanhead

      beanhead Well-Known Member

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      FWIW I threw in a quick-fuel 9.5 ....bingo. That got me right where I needed to be. The quick fuel ones have four slots to flow fuel instead of just two, how much of a diff that makes, I don't know. Sorry you've got more work to do to get there but I bet it'll be a monster!
       
    • coloradodave

      coloradodave FBBO Gold Member FBBO Gold Member

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      Yes...
       
    • coloradodave

      coloradodave FBBO Gold Member FBBO Gold Member

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      You might be putting too much faith in your A/F gauge. I've had both brands of the common gauges and they are both slow to react. Any tipping of the throttle shows lean for an instant. IMO, the thing you want to concentrate on is the steady cruising A/F at the rpm you normally run at and the A/F at sustained wide open throttle. Cruising at 30mph and 11:1 ratio will drain your tank fast. If you are lean at sustained wide open throttle it's something to be concerned with. I still use the A/F gauge to set the idle, but rely on plug coloring after a wide open run to determine a too lean condition... old school for an old guy I guess.
       
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      • rrTor-Red

        rrTor-Red FBBO Gold Member FBBO Gold Member

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        Lots of videos on Youtube
         
      • wsutard

        wsutard Well-Known Member

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        All good info guys! Im learning a ton about carbs. Mainly that I should switch to fuel injection! (Does money still grow on trees?)

        Reporting back on changes:
        Changes made:
        Swapped in the 76 jets (from 72)
        Swapped in the 8.5 PV (from 10)
        Moved the float level back down to half

        Took a drive and it doesn’t lean out on acceleration but I’m kind of rich on cruise which is what I was trying to fix in the first place. Video of cruise is below (sorry for the vertical video). I’ll go take a longer drive a little later when the traffic dies down.



        @beanhead @68 HEMI GTS regarding my advance. When I had the engine dynoed it liked 33 all in. Anything more and it didn’t respond or lost some power. 33 all in is 12ish at idle for me. I do have a new MSD distributor so I might be able to change he the all in number and get a higher idle advance. I’ll look into it.

        @coloradodave Im rather certain the my gauge is very accurate as I have felt lean surges that correspond to exactly what the gauge is telling me. However, this also crosses my mind prior.
         
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        • 68 HEMI GTS

          68 HEMI GTS Well-Known Member

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          Yes, leave total the same. Shorten the curve with more initial. Back to the carb, it would really help to know all the orifice sizes including the air bleeds. Takes numbered drills though to do that. It doesn’t look that far off, just gonna take more than jets to get it really tuned in.
           
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          • wsutard

            wsutard Well-Known Member

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            I was wrong on my advance. Forgot I bumped it to 18 initial and 36 all in. No ping.

            I’m at the point where I don’t want to dial down the jets anymore for fear of lean out on acceleration but I’m still low 11 high 10 on cruise rpm.

            Question, what effect will enlarging the PCVR provide? I know it only comes into play once I drop below 8.5 vacuum. But will that help me fatten up my acceleration on the primaries if I jet down some more to get a better cruise?
            If so will it fatten up my entire band of acceleration on primaries only?

            Also, anyone used an aftermarket metering block like this? https://www.summitracing.com/parts/pro-67166c/

            From research it looks like my other option is to keep my jets where they are and drill holes in my butterflies to allow more air during cruise.
             
          • 68 HEMI GTS

            68 HEMI GTS Well-Known Member

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            Holes in the butterflies are for idle issues. They provide bypass air to keep the throttle plates closed enough so the carb stays on the idle circuit. They won’t change the cruise A/F. Enlarging the PVCR will fatten the carb up anytime the vacuum is low enough for the PV to open. It’s the same as adding jet. Usually that’s for heavy acceleration. You need to decrease fuel draw through your idle/transfer circuit for your low RPM issue. There’s 3 ways to accomplish this. Smaller IFR’s, more idle air bleed, and transfer slot restriction. Can takes a combination of adjustment on all 3 depending on the calibration of the carb. Aftermarket metering block doesn’t have any advantage unless your willing to start modifying orifices.
             
          • wsutard

            wsutard Well-Known Member

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            Update, still no fix. Here is what I have done lately and what I am experiencing.

            Purchased a proform metering block with adjustable PVCRs.
            Jetted down from 78 to 72 (cruise a/f is good at 72 but is even a tad rich.)
            Enlarged the adjustable PVCRs from stock of .070” to .085”.

            Zero change to the lean out issue. However, I can tell that it is getting much more fuel from the PVC once the lean out goes away.

            To clarify the issue, I lean out as soon as I give ANY throttle. 1% throttle change will lean me out to above 18a/f until the extra fuel comes.

            I believe that my issue is only at the transition from cruise to pvc fuel flowing.

            I thought this is what the accelerator pump was for, however, I have increased to a 40 nozzle on the pump and ensured that it was calibrated correctly and that the pump was working.

            I have not touched the cam of the accelerator pump. I’m still on the stock black. Maybe there is a can that squirts fuel earlier than the black?
             
          • 68 HEMI GTS

            68 HEMI GTS Well-Known Member

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            That’s because you keep jetting it way to lean.
             
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            • wsutard

              wsutard Well-Known Member

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              Im getting all mixed up on this. I just reread your posts and I didnt even address what you suggested. Where do I pick up orifices that small?
               
            • beanhead

              beanhead Well-Known Member

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              Every engine likes a different pump cam, that said I've never liked the black one...it always seems weak. Experiment. Stick a blue one in, start back on a 31 squirter, re-calibrate the pump arm and just see how you like it.
              It won't fix the other stuff most likely bit you may like the response.
               
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              • 68 HEMI GTS

                68 HEMI GTS Well-Known Member

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                Blue 427 is my fav too!
                 
              • 68 HEMI GTS

                68 HEMI GTS Well-Known Member

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