Problem with Holley 4 bbl

Small Block Mopar Engine

  1. MOPAROFFICIAL

    MOPAROFFICIAL FABO Gold Member FABO Gold Member

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    in order to have power valve enrichment at idle you would have to be idling off of the main system -as in.. the primary throttle blades are too far open. Then theres the torn PV idea, too high float idea and torn and in the mains. However you wanna stack it.

    The Op needs to see if the secondary throttle blades are adjusted open too much.

    You need to take the carburetor off and on the bottom side there's a small little flat head screw to adjust the stationary position of the secondary throttle blade.
    At a glance of this thread I believe that's his problem and why he can close the primary all the way and it still idles. Vacuum secondary and double pumper have this feature ..or at least the ones I've seen. Now there is also or was some debate about fixed idle circuit on old holley vac sec carbs. About 15 yrs ago we argued over it .lol
     
    Last edited: Aug 11, 2021
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    • RustyRatRod

      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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      It could be that, but "I thought" he already addressed that issue. Maybe not.
       
    • MOPAROFFICIAL

      MOPAROFFICIAL FABO Gold Member FABO Gold Member

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      He says they're "1/3 of a turn open"
      Close them or make'em 1/8 of a turn.
       
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      • RustyRatRod

        RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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        I had to close mine ALMOST to the point of sticking. I MEAN REAL CLOSE. I got them to stick closed, and then like TWO DEGREES at the time snuck up on it till they didn't. Other than that, it was idling way high. Now it'll idle down till it dies on the primaries.
         
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        • dart_68

          dart_68 Well-Known Member

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          This is a carb that was rebuilt.refurbished by a professional vendor. I was running this carb on this engine before I rebuilt it. It has a stock 1990 roller hydraulic cam and mixture adjustments worked. But it also had way more idle vacuum too.
          I can get the mixture screws to affect the idle now as it should but almost no change in vacuum. I have them out about 3/4 turn. More in and it dies. I think I had the secondaries open too far before. We'll see how it runs when I get the chance to drive it.
           
        • RustyRatRod

          RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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          That could have been it. See my comment above about how I adjusted mine.
           
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          • AJ/FormS

            AJ/FormS 68 Formua-S fastback clone 367/A833/GVod/3.55s FABO Gold Member

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            WIKI says Lakewood Colorado is at 5518 ft elevation. That in itself is a problem.

            For a short time, I ran the 292/292/108 Mopar cam in my 367(11.3Scr at that time.). The beast measured 249@.050 on my equipment. It idled at 10/11" at 750 at my 930ft elevation. It would idle down to 600 at about 8* advance. I normally ran it at 14*. Mine needed the Transfers to be a lil taller than wide, not much. Holley 750DP. I ran it with the secondaries closed up tight but not sticking. She asked for one small bypass hole in each primary blade of about 3/32. 4/32 was too much, and I had to solder them shut and start over.

            you said; "PCV is connected to the throttle plate port on the back of the carb and gets full manifold vacuum."
            Is this correct? I thought all Holleys had the PCV port on the front? The back port is for powerbrakes. If you run the PCV to the back, then the back cylinders will run lean. When you run the PCV to the front the air mixes with the transfer fuel and everybody gets a fair deal.
            You said;
            Duration @ .050 - 235/247
            Lobe separation 110
            Intake center line - 106
            This looks sortof like a Whiplash/Thumpr, with a huge 12* split, but the LSA of 110 is too wide to be .
            My current cam is 230/237/110@.050 and looks to be about one size smaller. It idles at over 11", and will pull the Barracuda along on flat level hard ground at 550 rpm @5* of timing. It will go to 500. I still have that same 750DP on it, but the holes are ALL soldered up now.

            If I had to guess I would say that your intake is sucking oily air from the valley. You can prove this easy enough; just flip the PCV out and plug the hole, and plug the breather. Then put a vacuum gauge on the dipstick. Start it up, and the engine should IMMEDIATELY begin to build pressure Shut the car off before it goes past 3 psi, else you risk blowing the rear cam plug out. If you have vacuum there, that is NOT right.The intake has to come off.

            But if there is NO unmetered air entering the engine, and the timing is between 14 and 18 degrees; then I would suspect .................
            Oh wait, I have never tuned an engine at 5518 ft elevation, so IDK, I can't help you man. Maybe 5inches at 5518ft elevation is correct, IDK

            IMO, with the transfers square and the secondaries barely cracked, the engine should not be running in the first place. If it was sucking air somewhere that air has NO fuel in it, so it would just be worse; and the mixture screws would be working over time to keep up.
            My next guess is that the PCV running in the back is drying those back cylinders up, and she's running on the front four, dragging the others along.
            With an IR gun check the idle temps of the back cylinders versus the fronts.
            If it was me, I'd go look at that carb again; it should have a PCV port on the front.
             
          • 65Val

            65Val Average Length Member

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            You do not need to drill primary blades. Theres a tiny screw, accessible from the bottom of the baseplate, that can be turned to open the secondary blades slightly, then you can close the primaries down to where the idle mixture screws will function again.
             
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            • RustyRatRod

              RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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              I agree. I've never liked doing it. There are different and better ways.
               
            • 70dart340

              70dart340 FABO Gold Member FABO Gold Member

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              Initial timing is everything. I just built a slightly hairy 351 Cleveland for my best friend. He insisted on setting the timing to #%!C factory timing, 6 degrees BTDC. I told him he has a much bigger cam, and Cobra Jet heads. After dicking around for months, he allowed me to change it to 10 degrees BTDC. What a difference. Set the timing, and tuned the Holley from there. It idles at 950 in park, and drops to 775 rpm in gear. Tuned the accelerator pump, and no throttle lag. We did change the accelerator cam on the Holley, but it's a ripper now. I apologize to my Mopar Brothers and Sisters, but basic tuning is where I start. A laptop is useless on these old motors, and I love it.
               
            • RustyRatRod

              RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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              No apology necessary. Clevelands can be beasts. I have a disassembled 70 M code 4V Cleveland sittin in the spare bedroom, complete with the BIG port closed chamber heads.
               
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