318 Spread Bore No Idle

Fuel and Air Systems

  1. JedIEG

    JedIEG Well-Known Member

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    I have a Holley 4165 that I rebuilt for my 318. I am not having any luck with getting the car to start. If I pour gas into the engine or hit the accelerator pump 3-5 times, I can get the car to start, but it shuts off after a second and will not refire unless I hit the accelerator pump a few times. The electrical seems to check out (brand new wiring harness modules, coil, timing light flashes when turning over)
    ect.). I can see some fuel coming out from around the base to intake so I am assuming I need a new gasket. Is that really enough ofa vacuum leak to cause it to not Idle at all?
     
  2. Lefty71

    Lefty71 Well-Known Member

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    Yes
     
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    • artr8

      artr8 Active Member

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      The air/fuel mixture to start and idle from cold needs to be high 10:1 or so with any carb. After the car warms up, anything in the range of 12-17 will keep the car running with varying levels of exhaust output.
      [​IMG]
      Don't ignore the possible gasket leak, but....., be prepared to look elsewhere also.

      What other vacuum potential problems could be the source? Did you miss the pvc or brake vacuum hoses? Was the intake also changed out? Most intake leaks will not keep the car from starting but will make you chase your tail once you get it running. Gaskets need to match the port size, 340 and 360 are different from the 318. (Assuming stock heads).

      Possible ignition condition. Mopars use a separate circuit for the run stage. During start, the ignition bypasses the ballast resistor and puts 12 volts to the ignition coil. After starting and the key is released, the voltage drops via a 5 ohm resistor (dual ballast for electronic, single for points).

      Here is a stupid one that got me twice in the last 20 years; the condenser on a points dizzy went bad. Intermittant start and run problems.

      No matter what, carefully check each point that it needs to make it run... ignition with key on but not in start mode, fuel to the carb and through the carb, any changes in camshaft timing, verify correct firing order.

      Before I take off, if you have another dizzy around, hook it up to the connections, pull your coil wire and set with 1" gap to any ground, turn the ignition on, and spin the spare dizzy. If it sparks like 4th of July, you have eliminated the ignition. If not, correct before you go any further.
       
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      • JedIEG

        JedIEG Well-Known Member

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        Every part of the ignition system is new and I have 2 new style ignition modules and single ballast resistors, even the stock module and duel resistor. Distributor is new. Coil is new. I know electricity is going through the plugs.
        Starting with what I know is wrong: I pulled the carb off last night and the manifold, gasket and under side of the carb were soaked with gas. The gasket is too thin in my opinion (less than paper thin almost), I don't think it ever had a chance of sealing. My dad has a few factory Holley 2bbls that have a nice 1/4 inch fiber/carbon gasket. Is there a source for those for a spread bore? Will a Q-jet or TQ base gasket work?
        Thanks for suggestions.
         
      • 747mopar

        747mopar FBBO Gold Member FBBO Gold Member

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        You should be able to pick up the thicker gaskets at a local parts store but no reason a thin gasket shouldn't seal. Check your carb and intake for flatness then make sure your not running out of threads on your bolts/studs before it snugs down.

        Also never assume new means good, I've had more faulty parts in the last 5 years than I've likely had in my whole life.
         
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        • artr8

          artr8 Active Member

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          The Q-Jet or TQ base gaskets should work. Verify by lining up and look at the bottom of the carb. Trimming may be required around the throttle blades but will be minimal. Done it plenty of times. I prefer the thicker gaskets to take up any variation in surface.
          Let us know of your success. Cheers.
           
        • miller

          miller FBBO Gold Member FBBO Gold Member

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          Make sure the carb base surface is actually flat. A straight edge will tell ya...
           
        • JedIEG

          JedIEG Well-Known Member

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          Agreed. That's why I have 4 control modules and ballast resistors. The first new one died so I bought two more, one is Mancini Racing's so I'm banking on them wanting to keep a good reputation if I have problems.

          Supprizingly, I got a 1/4" gasket from O'Reilly's after calling every other box store. I need to make longer studs now though.

          On the carb, the transfer slots look about right compared to the 4160 I have with the throttle closed. Is there anything else I should check on my carb before putting it back on the engine?
           
        • Ron H

          Ron H FBBO Gold Member FBBO Gold Member

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          This may not be an issue with you here; but when I had put on a 4bbl to my stock 318 intake I found out that the throttle plates were hitting the intake ports requiring a thicker spacer and this solved my problem.
           
        • JedIEG

          JedIEG Well-Known Member

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          Well I have done some more testing and replaced the gasket with a 1/4" thick one. No more fuel dribbling from the carb base. Just replaced the plug wires (OE from a '68 340) with 8mm JEGS wires I bought to be very sure that variable was eliminated. Retimed the distributor to a little advanced of tdc verifying with the cap off. Clamped off all vac hoses except the advance. Still not wanting to run. I'm thinking there is an issue with the idle circuit of the carb. Here's my starting procedure:

          1. Charged the battery to full on the tender for full power to the coil.
          2. Two full squirts from the accelerator pump.
          3. Key on. Then to start position.
          4. Engine fires in a 1 -2 revolution.
          5. Key to run
          6. At the same time, Engine runs for a second then stalls.
          7. Wait for engine to stop rotation, then key to start. No more fuel given through the accelerator pump.
          8. Engine turns over, sparse fringing of a random cylinder every 3-5 seconds.
          9. Key off.
          10. 2 squirts of the accelerator pump and... (Repeat steps 2-5)...

          Since its firing after the accelerator pump, I'm assuming not enough fuel is getting in through the idle circuit. I have tried adjusting the idle screws to no avail. What can I check?
           
        • coronet68mx

          coronet68mx FBBO Gold Member FBBO Gold Member

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          Do you have another carb that work in another car to try ?
           
        • JedIEG

          JedIEG Well-Known Member

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          Unfortunately no. I have a 600cfm 4160 I got free with the car that I rebuilt 5 years ago. I tried it a while ago and it was leaking like a stuck pig so I swapped it for this 4175 I rebuilt over the winter.
           
        • coronet68mx

          coronet68mx FBBO Gold Member FBBO Gold Member

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          Spark , air and fuel, seems obvious the lack of fuel in the cylinders, disassemble the carb again and go step by step in the rebuild process imo.
           
        • coronet68mx

          coronet68mx FBBO Gold Member FBBO Gold Member

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        • Don Frelier

          Don Frelier FBBO Gold Member FBBO Gold Member

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          ART8 suggested this a while ago.

          Perhaps I'm reading this wrong but sounds like it starts while cranking, then quits in the run position.
          So are you getting spark when the ignition is in the run position?
          It's possible that you have a bad bulkhead wire connection or ignition switch problem.
          As stated one way is to either take a spare distributor or lift yours out (note rotor position).
          Turn key to run and spin the shaft with your fingers with the coil wire 1/4" away from a good ground.
          See what you get should be a blue crisp spark. Not yellow and lazy.
           
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          • 1967coronet

            1967coronet Well-Known Member

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            Once it dies , dont crank and check your fuel bowl level .
            Also once it fires when it does keep dribbling some fuel in the top to keep it running for awhile to take the ignition question out of play.
             
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