318 carb issues

Discussion in 'Mopar Performance Issues' started by BigBlockMopar28, Dec 25, 2017.

  1. BigBlockMopar28

    BigBlockMopar28 Well-Known Member

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    318 in the ram was bone stock with all smog, removed the smog stuff and took the a/c off, installed a 340 alum intake and 600 holley street warrior vacuum, timing is good for sure. Long story short, had to tie off the choke because it would want to idle high when the truck was perfectly warm, and did not want to idle down for anything except on a few random occasions. It doesnt like to idle on cold starts without alittle pedal assistance for a min, i guess thats normal for one without a choke? Idles pretty low in gear (truck shakes some), but any higher and it wants to slam into gear. Has a bad flat spot around half throttle, especially when coldish. If i push past the flat spot around 3/4 throttle it will pull just fine, just has that flat spot that has me stumped. If i pedal it some in that spot it helps it for just a sec, leading me to believe its starving for fuel, but any adjustment on air/fuel makes it worse, its very sensitive. Fuel filter had some resistance, put a new one in and it barely changed anything. Carb is brand new, back bowl wanted to leak just a tad but i tightened it up and it seems to be ok now. I'll add that around that flat spot it really wants to hesistate, almost stalls out with to much pedal when cold. Idles and revs just fine, only acts up under load. Any ideas? New to this stuff so any help is appreciated. Thanks FABO!
     
  2. DFX 340 Duster

    DFX 340 Duster FABO Gold Member FABO Gold Member

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    What model of carb?
     
  3. AJ/FormS

    AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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    Let me get this right; The vacuum and timing are good for sure,
    But you have all these problems now, that you didn't have before...........
     
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    • Tooljunkie

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

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      Type of choke on this carb? Mechanical/electric?
      Engine cold,choke goes closed,vacuum applied to choke break and it should pull plate about 3/16”. Fast idle should be set on second highest step.
      It likely came kind of dialed in from stock but choke needs to be adjusted full open at operating temp.
      Accelerator pump may play a part in this too.
       
    • BigBlockMopar28

      BigBlockMopar28 Well-Known Member

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      Holley street warrior, 600 vacuum
       
    • BigBlockMopar28

      BigBlockMopar28 Well-Known Member

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      Correct.
       
    • BigBlockMopar28

      BigBlockMopar28 Well-Known Member

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      Electric, ill have to take a look at adjusting that.
       
    • krazykuda

      krazykuda FABO Gold Member FABO Gold Member Technical Editor

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      Also make sure to get a good 12 volt source for the electric choke... Do not get power from coil or ballast out for choke...
       
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      • Krooser

        Krooser Reform School Graduate

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        What year truck? Vacuum advance working ok?
         
      • BigBlockMopar28

        BigBlockMopar28 Well-Known Member

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        87, and yes it should be.
         
      • BigBlockMopar28

        BigBlockMopar28 Well-Known Member

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        Ill add that currently the air/fuel is rich to the point where it shoulf probably be flooding, just so that it gets enough fuel. Tried to call holley to see what they would say, turns out they are still closed for holidays
         
      • BigBlockMopar28

        BigBlockMopar28 Well-Known Member

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        This just dawned on me... could this be a fuel pump issue? Only acts up in that one spot, but i guess it could kind of make sense. Lol
         
      • RustyRatRod

        RustyRatRod Just another dumbass. FABO Gold Member Technical Editor

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        "Timing good for sure" "It should be" when asked about the vacuum working.

        Exactly where is the initial timing set? Have you actually checked the vacuum advance for operation? Although it will not necessarily cause your issue, it could be a contributing factor if the diaphragm is ruptured and it has a vacuum leak there.

        Word to the wise:

        Never say "this is good" or "that is good"when asking for help. Because more than likely that's where the problem lies. Unless you're willing to be open to those possibilities, then we may as well stop right here and now.
         
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        • BigBlockMopar28

          BigBlockMopar28 Well-Known Member

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          Old thread but the problem is still here after a new timing chain (old one slipped shortly after this), and new fuel pump. Air/fuel screws are set at 1 1/2 turns out, that seems to be where it likes. Same issue, no issues in neutral, but big flat spot under load around 1/2 throttle. Different ignition as well, lean burn was swapped in favor of a non digital msd 6al
           
        • dusted

          dusted Well-Known Member

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          Sounds more like a jetting issue to me. Is the intake a single plane or dual? If single plane it needs a lot more of a pump shot or bigger squirters. Check the jets also.
          If it wants to idle high look for a vacuum leak. I’ve been in the same boat when converting mine from TBI to carb

          59E25BAD-4A61-4B34-B6E1-8542E4AC4373.jpeg
           
        • BigBlockMopar28

          BigBlockMopar28 Well-Known Member

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          Dual plane. But good idea on vacuum leak, that may just be the issue
           
        • oldskool979

          oldskool979 FABO Gold Member FABO Gold Member

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          IIRC the 87 318 ram was equipped with vac controlled emission and electronic spark control. (lean burn) I would bet that the distributor advance (mech and vac) is calibrated for those controls. I would ck your distributor to see if you are getting the advance that you need.
           
        • scott657

          scott657 Well-Known Member

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          try it without any vacuum advance
           
        • BigBlockMopar28

          BigBlockMopar28 Well-Known Member

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          Msd 6al with old style vacuum advance currently, but it is a former lean burn truck. And will do scott
           
        • BigBlockMopar28

          BigBlockMopar28 Well-Known Member

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          With or without vacuum advance makes no difference, timing adjustments made no difference, and no vacuum leaks on any hose/line I could find. What is a good baseline setup for the accelerator pump? That's the only thing I haven't touched on this one and i'm not too familiar with them.
           
        • BigBlockMopar28

          BigBlockMopar28 Well-Known Member

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          It just occurred to me that the pump nozzle size could be off... From what i've read my carb currently has a #31 nozzle, would it be best to try a bigger nozzle or smaller at first? Kind of torn because holley says smaller nozzles are best for heavy vehicles and/or vehicles with tall gears, and that bigger nozzles are best for vehicles with good power to weight. The truck isn't light compared to an A-body (its almost 5,000lbs), but it does have 3.55's and a 727. Stock 318 w/ dual plane 340 intake and 600 holley vacuum. Choke is no longer a factor as it has been tied off. TIA