318 2bbl won't idle without choke

Small Block Mopar Engine

  1. Tylinol

    Tylinol Active Member

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    Been chasing a carb issue on my 69 Barracuda. The car is a 2bbl Carter 318 with the original engine and carb. I've been bringing it back from a long slumber since buying it in April.

    I've replaced the entire ignition system (plugs, wires, ballast resistor, distributor with all internals, coil) and have the timing set to 10 BTDC. I've rebuilt the carburetor with new gaskets and a general cleaning.

    The car will run and drive pretty well if the choke is at least ~25% of the way closed, albeit with a slightly high idle. Other than feeling like it's a bit more sluggish than it should be, it's not bad. However, even when warmed up all the way it won't idle with the choke open. If I bump the idle speed up a bit, I can get it to very roughly idle, but touching the gas kills it right away.

    The mixture screw is set 1.5-2 turns out, but oddly enough adjusting it has no effect on the idle. Several turns in either direction seem to do nothing.

    I've done propane torch / carb cleaner / cover the carb throat tests for vacuum leaks and haven't found any yet. Any other places I should look?
     
  2. abdywgn

    abdywgn dismantler

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    vacuum advance canister on distributor
     
  3. j par

    j par Well-hung Member

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    I would be looking for a massive vacuum leak...
     
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    • silversedan

      silversedan Well-Known Member

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      carb is still dirty, clean all passages again.
       
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      • TT5.9mag

        TT5.9mag Two atmospheres are better than one

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        This right here. If you don’t have any vacuum leaks then the carb still has trash in it. The idle mix screws are useless when you crank the curb idle screw in to get it to idle.
         
      • Tylinol

        Tylinol Active Member

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        Thinking this might be the ticket...I got it to very barely idle with the choke off and took a look down the carb. The right hand side had a steady drip from the jet(?) onto the throttle plate ares, but the left hand side had nothing.
         
      • TT5.9mag

        TT5.9mag Two atmospheres are better than one

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        If fuel is coming out of the booster the float level is too high or the needle and seat are dirty or fuel pump pressure is too high. I’m betting dirty needle/seat.
         
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        • MOPAROFFICIAL

          MOPAROFFICIAL FABO Gold Member FABO Gold Member

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          Spray some water or WD-40 around and on the sides of the carb to see if the idle speed drops.

          And for others if you ever wonder if your carburetor has a vacuum leak you put your hand over the top of it and if it runs better.... that's a vacuum leak at the carb or base of the carb
           
        • 66Vcuda

          66Vcuda Member

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          Have you corked off the power brake booster and/or the PCV?
           
        • Tylinol

          Tylinol Active Member

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          Interesting - I did have a clog in one of the little brass tubes attached to the triangular block that goes in the middle of the carb (I'm not sure what the proper name is, I've seen it labeled "idle fuel pick up tube"). I unclogged it and now it idles easily with the choke off and gas is dribbling from both the cylinders on the "venturi cluster" (again, not sure of the proper name).
           
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          • dano

            dano Evil Handy Man

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            Did you try lowing the float height?
             
          • Tylinol

            Tylinol Active Member

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            I just took the top of the carb off after running the car a while to check it. With the carb full of fuel and the floats as closed as they can go, it's 1/4" from the top of the carb body - maybe ever so slightly less, actually. That should be correct, right?
             
          • toolmanmike

            toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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            THere are measurements in the kit and instructions for float level and float drop. Those adjustments are fairly critical.
             
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            • Tooljunkie

              Tooljunkie King of cobble/master of the broken bolt FABO Gold Member

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              My 2 bbl was dribbling fuel also, as i lowered idle speed the dribble stopped and i was able to get it idling a little nicer. Seemed rich before.
               
            • AJ/FormS

              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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              Yur timing is IMO lying to you. Crank in the ignition timing and close the speed screw until the throttle blades get back down on the bottom of the transfer slots, and the mixture screws start working again. Then check the manifold vacuum . If it ain't over ~16 inches at 650(N/P), then check the cam timing.
              If it is over 16, then prove the index TDC is true TDC #1 cylinder on compression stroke.
               
            • RedFish

              RedFish Well-Known Member

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              If you're running today low octane puppy pee pump gas, after you get fuel/air mix and everything else right, try bumping base timing up to about 14. You'll need to back off the idle screw a little to lower rpm again. Performance gets better.
               
            • Tylinol

              Tylinol Active Member

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              Well the saga continues - I took the carb apart again and am now confident that all passages are clean and the float height is at 1/4". I also realized I was missing the smaller check ball that goes in the venturi assembly. Now, the car runs worse than ever (won't rev at all), and fuel still drips from the venturis at idle.

              When I was re-rebuilding it, there was a small gasket that I had installed on the bottom of the power piston. It's like a small rubber cup that came with the kit. However, it doesn't seem to really stay attached to the piston when the piston moves upward and just kind of hangs out there at the bottom of the barrel. It also doesn't appear on any of the diagrams as far as I can tell. However, I'm going to try putting it back in since it's the only thing I changed besides cleaning passages and putting that check ball in.

              I'm also skeptical of the fuel level. I know the floats are adjusted right - I've triple checked. When I took the air horn off, the bowl wasn't overflowing or anything like that either. If I pushed down on the floats by hand, I'd get a spray of fuel into the carb bowl, so I know the needle is seating at least with the engine off. However, when running the top gasket between the body and the air horn gets visibly wet with fuel. Is it possible that the running fuel pressure is too high and forcing its way past the float valve?
               
            • Tylinol

              Tylinol Active Member

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              Another update - this is almost certainly a fuel pressure issue. I'm not sure how the car ran as well as it did before (maybe the high idle speed and the missing checkball somehow made it work, idk) but the pump is overwhelming the floats. I cranked it over for a few seconds and fuel was coming out of the throttle shaft and dripping form the venturis even with the engine off. I pulled the top cover right away and saw that the fuel level had risen past the floats and was still rising (presumably all the way to the top, which is how the gasket got wet). After a while, fuel drips back out of the throttle body into the manifold and the fuel level stabilizes. I'm guessing this is because the residual fuel pressure slowly drips to where it's not overwhelming the floats anymore.

              I replaced the pump with a new mechanical unit when I first got the car. Sounds like I need to adjust the pressure with some sort of inline regulator?
               
            • AJ/FormS

              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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              There is no gasket at the bottom of the power piston; this will only serve to raise the metering rods and make it run rich.

              There is supposed to be a horseshoe-shaped flat metal bar installed onto the float pivot. When you put the top onto the carb, it pushes the float down and locks it in place. Is yours in there?

              The fuel in the bowl is constantly at or near the "boiling-point". and so there are vapors floating in the bowl any time the temperature is near 90*F. They float up and condense on the gasket,making it wet. That is normal. It is also normal for that gasket to be visibly wet at the squeeze-out, whenever you shut the warm engine off.
              It is NOT normal for any fuel to be leaking out from the throttle shafts nor boosters.

              Leaking boosters point straight to one of two things; 1) a very high fuel level, or 2) a very high idle rpm.

              A very high idle rpm is a direct result of;
              1) you set it that way, because that's the only way it would stay running, because;
              A) of the gas dripping into the intake, or
              B) because of retarded ignition timing, or
              C) because the cam-timing is off, and the vacuum signal is so darn low.

              2) a vacuum leak in conjunction with the leaking fuel. or
              3) very advanced timing.
              4) a Hi float level (lol) that causes you also to screw in the speed screw, in a hopeless attempt at giving it the extra air to burn off the fuel.
               
              Last edited: Sep 17, 2020
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              • Tylinol

                Tylinol Active Member

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                Just ran outside to double check - it's on there, with the round side facing up and the "legs" against the float pin
                 
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                • Tylinol

                  Tylinol Active Member

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                  So, I tested the floats again. They're brass floats - I put them underwater and turned them every which way. No bubbles and no sloshing when I shook them, so I'm sure they're fine. I took the needle and seat out and cleaned them again. Both look good with the little rubber tip intact and free of debris. Float is set to 1/4". Got a fuel gauge and checked my fuel pressure, and it's 6psi.

                  Gas still comes out the throttle shaft and drips from the venturis. I'm running out of ideas!
                   
                • Phreakish

                  Phreakish Well-Known Member

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                  Clean isn't everything. It's possible for it to leak for many reasons. I'd either replace the needle/seat proactively, or attach a hose to the fuel inlet and fill the hose with gas while holding the needle into the seat (lightly), and see if the needle/seat leaks at all - even if it doesn't leak at rest, it may leak under pressure still. I've done this with lots of small engine carbs and 10/10 the needle leaks and has been my issue.
                   
                • TT5.9mag

                  TT5.9mag Two atmospheres are better than one

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                  How are you measuring float level? You’ve said a few times that they are 1/4” and perfect, but maybe there is something procedural going on.
                  https://www.carburetor-parts.com/
                  Has a lot of useful information.
                   
                • Tylinol

                  Tylinol Active Member

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                  I turn the carb upside down and measure from the middle of the top of the float to the top of the carb body, as described in the FSM. The reason I'm almost positive it's not the float level is because when I take the air horn off after cranking, fuel is still coming in past the needle and the floats end up submerged after a bit
                   
                • TT5.9mag

                  TT5.9mag Two atmospheres are better than one

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                  Watch the video for the bbd carb float setting at the link I provided. Mike is a very knowledgeable carb guy and he’s doing it a different way.
                  “Lightly press the float tang down to seat the needle and measure the top of the float”. Now I’m not saying one way is right or wrong. I’m saying it’s different.
                   
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