Need help on new rebuild

Discussion in 'Small Block Mopar Engine' started by Lildart, Nov 7, 2018 at 11:39 AM.

  1. Lildart

    Lildart Well-Known Member

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    8D3F94E2-02EB-4DB3-8E14-1688BC2E635C.jpeg As the post says, HELP please.
    I have a 1968 340 fresh rebuild. Standard bore, .010 x .010 crank, heads all new with guides, valves, springs. I was able to reuse my factory 4 speed camshaft. I did not degree the cam. Factory iron externals. Exhaust, intake. Distributor is a rebuilt factory point. Was going to upgrade later.
    I started the engine and it seems to be very happy, but will not run on the idle circuit. Carburetor is a 600cfm Edelbrock. When choke is closed it will idle.

    So far, I tried a different carb Edelbrock. Timing is set at 10 btdc. Ran hot wire from battery to + of coil. Sprayed carb cleaner looking for leaks, pulled valve covers to ensure valves not hung open. Since I tried another carb and no difference I can eliminate carb issues. I retourqed intake thinking it may be sucking air from the underside.
    I used search button and read for 2 hours. I am lost , any ideas?
     
    Last edited: Nov 7, 2018 at 11:52 AM
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    • j par

      j par Well-hung Member

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      What is the timing at when it's all in? As in what is the highest timing degree you get? Like at 3000 RPMs
       
    • Lildart

      Lildart Well-Known Member

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      I have not checked total timing. I am not getting any backfire intake or exhaust. Throttle is very responsive, runs pretty good as long as choke is closed.
      I will check timing and post results.
       
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      • dano

        dano Evil Handy Man FABO Gold Member

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        Is your vacuum line to the distributor off the "spark port"? It should be on the port that has no vacuum at Idle.

        Is that hose connected to your PCV valve sealed at the valve?
         
      • Sterling

        Sterling Well-Known Member

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        It is running lean, so I would guess carburetor or vacuum leak. Could be leaking in the valley, were the heads and block resurfaced ? Maybe the idle circuit not working?
         
      • Lildart

        Lildart Well-Known Member

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        I have removed all the vacuum ports on the carburetor and put on plugs. Originally I had vacuum advance connected to port above throttle plates.

        I have tried 2 different carburetors, same with both.
         
      • Murray

        Murray FABO Gold Member FABO Gold Member

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        Sounds like engine is running lean as closing the choke makes it run better. Check for vacuum leaks which would include the intake manifold itself.
         
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        • Dubob

          Dubob Well-Known Member

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          Dumb thought on my part, does the passenger side exhaust manifold have the heat riser still? If so is it open?
           
        • Lildart

          Lildart Well-Known Member

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          The riser has been removed. No dumb thoughts in my opinion. I have been building cars for 30 years. This one has me stumped.
           
        • j par

          j par Well-hung Member

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          Still seems like the carb.
           
        • Mattax

          Mattax Just the facts, ma'am FABO Gold Member

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          Lets break this down. That way you can isolate the issue.

          Before that, clear away a few things.
          Has the engine been broken in? Say 20 minutes at 2000 rpm or whatever your favorite procedure.
          Initial timing was at what rpm?
          - Was this measured with or without vacuum advance? (should be without)
          How low of rpm would the engine run at before dying?

          Take a deep breath.
          Check the fuel level.
          Get it running at the lowest rpm it will run smoothly at.
          Check the timing again if needed.
          Adjust the idle mix screws in and out.
          - What happens? Is there response? Can the motor be shut off whith the idle mix run in? How many turns out to get it running smooth?
          All of this ^ is to see what ways the carb and fueling may be the problem.

          Add some timing and see if you can then slow down the engine with the throttle position (idle speed) screw.
          ^ This is to see if its timing related.

          Obviously there's spark, so it comes down to fuel, timing or compression. So the third thing to check will be compression. But I would start with the two above. If you have vacuum gage, it will show poor valve seating, so thats an indirect way to check the cylinder is sealing.
           
          Last edited: Nov 7, 2018 at 12:53 PM
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          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            Is this a generic rebuild, or the correct original '68 4 speed distributor?
            A factory correct '68 4 speed distributor is going to have a very quick advance curve in it. If the engine is set at 10* BTDC at 1000 rpm, it will have 0* around 700 rpm. That was on purpose to meet emissions at idle and still have good power off-idle as you put it into gear.

            You can give it a little more advance. You can do that safely because there's no load on it. Additionally, if its a factory curve, Plymouth spec'd it on the conservative side for heat soaked engines.

            This graph is based on the 68 Plymouth FSM. Dodge sometimes used slightly different initial and curve specs but were similar.

            1968-340-timing.png
             
            Last edited: Nov 7, 2018 at 12:56 PM
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            • AAndrews

              AAndrews Supercuda

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              Did you leave 12volt lead from battery on the coil? Not designed to run this way especially with points. This will probably cause arcing and pitting of the points with this setup
               
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              • Lildart

                Lildart Well-Known Member

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                I did it as a temporary test. I ran engine just long enough to see if it was a low voltage issue. It made no difference.
                 
              • AAndrews

                AAndrews Supercuda

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                I'm clutching at straws. What kind of fuel pressure do you have? Bad or defective fuel pump ? fuel pump rod eccentric worn or loose?
                 
              • nm9stheham

                nm9stheham Well-Known Member

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                A couple of simple tests to start:
                1. Put a vacuum gauge on the intake and measure vacuum levels. I would expect it to be up above 15 in on this setup, and very likely around 18". This sounds very much like a vacuum leak in the intake area or under the carb, and this test will show that.
                2. While running, pull the PCV out of the valve cover, still connnected to the hose and put your finger over the open end of the PCV. See if this helps the idle. If it is hung open at the cruise opening, then too much air will be pulled in at idle.
                3. Use a piston stop to find exact TDC to make sure your damper ring has not slipped.
                4. What is the points gap set to? It ought to be around .018" or so. A too-small gap will cause this exact symptom. Also, inspect the 'nubs' on the distributor (that operate the points' rubbing block) and make sure they are not worn down. If so, then the dwell (the time for the points to be closed to charge the coil before each spark) can never be set properly. This also causes this symptom.
                5. Did you put in a new condensor in the distributor?
                 
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                • Lildart

                  Lildart Well-Known Member

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                  You folks are giving some great pointers. The distributor is a reman I bought from Orielly auto. ( that’s not saying much for it) I will do some testing. As has been recommended and post my findings.

                  Thank You all
                   
                • Lildart

                  Lildart Well-Known Member

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                  I had to go out and buy a few tools. Garage fire a couple years ago really hurt with not having the proper stuff.
                  So at 800rpm choke fully closed. I have 18” of vacuum below plates. Above plates I have 2-3” tap the throttle and it jumps to 15”.
                  I pulled dizzy, it is new. Not a reman points are set at .018

                  I will continue and post as I go.
                   
                • 12many

                  12many Well-Known Member

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                  Are you sure you have the throttle blades set (via idle speed screw) correctly showing square transfer slots? (remove the carb to set) I'm thinking maybe with the choke needed for it to run you could be using the chokes fast idle cam instead?
                   
                • my5thmopar

                  my5thmopar Life Long MOPAR Owner FABO Gold Member

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                  I know you said another carb but did you block the brake port on the back? Just checking since others have overlooked it before. Block off all ports for testing and then do your leak checks. You’re getting good advice. Keep us posted.
                   
                • Lildart

                  Lildart Well-Known Member

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                  Fixed, this is embarrassing but to help others I will explain.
                  When I rebuilt my Edelbrock carb, the kit only came with an open gasket. I was not happy putting this on a 4 hole intake. My local supply store had a 4 hole but the holes were to small in the rear. So open gasket it was.
                  Tonight I removed the carburetor one more time. I wanted to see if I could see an imprint all around the gasket see if it was sealing. Then I look at the intake design and thought heck that won’t seal.
                  I take the 4 hole gasket and a razor blade and enlarge the rear holes. Put it back together and it runs perfect. Choke wide open and idles.

                  4C54F681-EB35-488E-A99D-C0321DA532A1.jpeg 12AC7AB0-CB82-48BA-BA0A-37E3874ED5DB.jpeg
                   
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                  • j par

                    j par Well-hung Member

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                    I think you may need a spacer to run that carburetor?
                     
                  • Lildart

                    Lildart Well-Known Member

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                    I need to do something. I am not crazy about the minimal surface area on the right rear of the intake.
                     
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                    • j par

                      j par Well-hung Member

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                      That intake was probably made for a thermoquad or something that fits in those holes and the Edelbrock doesn't likely. Get a 1 inch adapter spacer.
                      If I'm reading your problem correctly.
                       
                    • AJ/FormS

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

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                      The proper gasket for that is for an AVS and is about 3/8 thick, made of compressed paper with torque limiters in the corners.EDIT; more like 5/16 thick
                      Like the bottom one.
                      But I can't see why the top one wouldn't work in a pinch.
                      9265 or 9266


                      8136881-IMG_2035.jpg
                       
                      Last edited: Nov 7, 2018 at 10:08 PM
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