Rebuilt top end of engine now carb idles much higher?Please help

Fuel and Air Systems

  1. LovetheA's

    LovetheA's FABO Gold Member FABO Gold Member

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    So I finally had to time to address the issues I had to fix after relocating my dart in my move. So I have a 67 dart with 383 four speed. I swapped out the cast iron 915 heads for edelbrock rpm performers. Do to time constraints I previously put the edelbrock intake and speed demon carb back on to move the car. Now that I have a little time I decided to fix a couple asthetic things on the car. The car previously idled at around 1000 rpm. If I remember correctly it has a bit of an aggressive cam 484 lift 284 duration. I took off and reassembled the valley pan, edelbrock intake and demon carb and throttle linkage and I was careful to really clean all mating surfaces and torquing intake carefully but now the car idles around 1500 rpm. Also I checked and adjusted the timing. It has an upgraded electronic distributor and the timing is advanced to 36deg. It seemed to run the best at that setting after adjusting it. I tried to adjust the carburetor idle screw down but it won’t adjust any lower than what it is set at. I didn’t set up the original carb and throttle linkage. I took some close up photos of the linkage. My concern is two fold. Is the higher idle a result of a vacuum leak somewhere how can I figure out the problem and lower the timing to a more comfortable 800-1000rpm? I included some photos. Thanks
    Carl

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  2. LovetheA's

    LovetheA's FABO Gold Member FABO Gold Member

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    P.S. I included some close ups of the idle screw and the setup. I’m much more familiar with the edelbrock carburetors and I think speed demons are more like a Holley. Should I buy a vacuum gauge for testing purposes?

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  3. Dana67Dart

    Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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    Yes you should have a vacuum guage, a dwell tach, and a timming light.

    In your photos 2 #2 and 3 it almost looks like your throttle cable is bottoming out on the linkage. Could be binding and keeping your idle high.

    I assume you adjusted the idle stop screw out so to lower the idle.

    Also you may be at an rpm where your mechanical advance is pulling in speeding up the engine.
     
  4. RustyRatRod

    RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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    Where is your initial timing set? In other words, where is the timing at "idle"? If it's at 36* at idle, there's your problem. It should be "somewhere" between 12-20* at idle and I would go no more than 34* total all in by 2500 on a big block. Disconnect the throttle cable and start it up. See if the throttle cable might be holding the throttle open some.
     
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    • LovetheA's

      LovetheA's FABO Gold Member FABO Gold Member

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      I have to apologize in that I’m trying to learn as I go along. Sometimes I may need things explained to me in more detail to fully understand. Yes I tried to back off the idle screw to lower the idling rpm. It seems to only adjust down to where it is at now. I loosened the rear bracket holding the throttle cable to see if this was limiting the low idle. I also tried to push the idle setting lower with my hand and it is being limited at the bottom. What would make the engine idle higher after reassembly? I didn’t change any of the carburetor idle settings? Would a vacuum gauge allow me to determine if there was a vacuum leak. I don’t know what a dwell tach is or what it is used for?
       
    • LovetheA's

      LovetheA's FABO Gold Member FABO Gold Member

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      Rusty yes the initial timing is at 36deg at idle based on the timing light and when I tried to lower the initial timing it seemed like it was going to stall? I thought that initial timing was supposed to be around 15-30deg. I was confused by where it was set at? Did I not move the distributor far enough? I could of swore it was going to stall out if I tried to move it much lower. I made some marks on the engine block and the distributor so on reassembly when I put it back in and 1 cylinder was at TDC it seemed very close to what the initial timing was set at maybe 38deg it that possible? I know there are probably multiple things going on here.
       
    • furyus2

      furyus2 Well-Known Member

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      Simple test for a vacuum leak is to cover the carburetor with a rag. If it smoothes out, you have a leak. If it slows down, or stalls, it's not that.
       
    • RustyRatRod

      RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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      Sounds like you have something WRONG, or perhaps your timing light is incorrect. Number one plug is the one on the driver's side, in the very front. Is that where you are attaching the timing probe? Also, I think it's time to verify TDC with a piston stop and make DAMN SURE the balancer has not slipped. 36* at idle is too much (unless the distributor has been locked out from racing) and that could be a contributor. You're just going to have to do some diagnosis.
       
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      • LovetheA's

        LovetheA's FABO Gold Member FABO Gold Member

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        I had the heads off the engine and when I replaced the timing gears and chain I made sure the timing gears were lined up. The thing is if I remember correctly at #1 TDC the dots on the timing gears were top gear 12 o’clock bottom gear 12 o’clock. So they were in line but not dot to dot. Maybe when I initially pulled the distributor off #6 was at TDC and the dots maybe were right next to each other. That’s when I marked the distributor? When I put the cover back on it lined up at the zero mark when the piston in cylinder one looked to be TDC. Is it possible I dropped the distributor in 180deg out because it was Initially pulled out with #6 TDC? Yes I attached the timing probe to #1 cylinder. I trying to understand what could of happened.
         
      • LovetheA's

        LovetheA's FABO Gold Member FABO Gold Member

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        Is that why when I tried to lower initial timing to around 15deg it was going to stall out and will only run with initial at 36deg because it’s 180 deg out?
         
      • LovetheA's

        LovetheA's FABO Gold Member FABO Gold Member

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        If so how can I fix it? Just drop in distributor 180 deg out and timing should work out?
         
      • RustyRatRod

        RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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        12 and 12 is correct for power stroke on number one. You line up dot to dot simply for convenient's sake to line the dots up. That's on number 6 power stroke, so, if you want the distributor in correctly with the dot to dot aligned, you drop the distributor in point to number 6 and you're good to go.
         
      • RustyRatRod

        RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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        No. Doesn't it run now? It will not run at all 180 out.
         
      • LovetheA's

        LovetheA's FABO Gold Member FABO Gold Member

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        Yes it runs now. So if it wouldn’t run at 180deg out then that’s definitely not the problem. I just don’t understand why the initial timing seems to only run up that high? When I tried to turn distributor and lower initial timing it sounded like it would stall. Well back to the dressing board.
         
      • LovetheA's

        LovetheA's FABO Gold Member FABO Gold Member

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        Furyus2
        It’s interesting about what you said about covering the carburetor to check for a vacuum leak. I tried to use my hands to block the air flow into the openings of the speed demon carb to see if it affected the way the car idled. Cupping my hands together over the top of the carb didn’t change the idle at all?
         
      • LovetheA's

        LovetheA's FABO Gold Member FABO Gold Member

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        So I did more research and possibly I’m not understanding how to set timing properly. If the avg factory initial setting for a standard 383 Mopar at idle is around 12deg BTDC does that mean that the timing is advanced 12 degrees? It’s advanced because it’s occurring 12 deg before the piston on cylinder #1 is at the very top of the cylinder before it begins the journey back down on the power stroke? If thats the case then the timing marks on the cover will show that it’s firing about 12 deg before the zero mark on the timing cover. This will show up on the dampener as the mark is 12 deg counterclockwise before the zero on the timing cover? Should the setting on the timing gun be at 12deg as well? To advance the timing further you turn the distributor clockwise which is the opposite direction of the engine rotation. As a result the mark on the dampener would show up further back counterclockwise on the wheel. Do I have this correct. Sorry about the rudimentary questions but I’m trying to learn.
         
      • LovetheA's

        LovetheA's FABO Gold Member FABO Gold Member

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        I’ve decided to buy a piston stop from Mancini. I’ll put it in cylinder #1 front drivers side. Mark the total distance traveled for the piston and in the middle is TDC. Then to make sure dampener is set correct it should be at zero on timing cover at TDC. I think that is a must do for me on this engine.
         
      • jau126

        jau126 '65 Dart GT 273 904

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        Do one or the other. Either set your timing light to 12 degrees or what ever initial timing and look for when it is zero on the balancer as your timing light is dealing with the advance. Or leave the timing light at zero and look for 12 degrees on the balancer.

        Also make sure your vacuum advance is disconnected (and plugged) when setting your initial just in case it is adding timing.
         
      • AJ/FormS

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

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        You did not mention degreeing the cam with either the old chain nor the new chain. That opens the door to thinking that if the two were not installed at the same ICL, then the cylinder pressure will not be the same.
        A 1 degree difference can equate to 1.5 psi difference. So 4 degrees could be 6psi. If your engine only musters 130psi, on the compression test, then 6 psi equates to about a 5%pressure change. This is very significant depending on which way it went.
        And it will affect the entire tune.
        But then, since you didn't degree the cam, you have no proof that the cam is anywhere near to where it is supposed to be. You may even, accidentally, be off one tooth. And that will wreak havoc with the tune.
         
      • LovetheA's

        LovetheA's FABO Gold Member FABO Gold Member

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        AJ/Forms
        Is there any possibility that before I deg the cam I first find TDC with the piston stop. Then at least I know if the timing on the dampener coincides with the timing cover marker. Try to reset the timing maybe I did it incorrectly or the dampener is off. I have no idea how to deg the cam but I’ll have to learn if the first steps don’t fix the issue. I also bought a vacuum gauge and can check for a vacuum leak and check cylinder pressure also to see if that’s way down. I’m dreading having to degree the cam because I’ve never done it before.
         
      • LovetheA's

        LovetheA's FABO Gold Member FABO Gold Member

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        Can you degree the cam with the water pump and timing cover on if I have determined that the damper and timing cover are dead on? I don’t want to tear apart the engine for the third time. Sometimes learning this stuff is a royal pain in the ass doing the same things several times.
         
      • RustyRatRod

        RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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        I've explained how you need to check that out. You need to VERIFY TDC with a piston stop. That way, you can compare true TDC to the balancer and see if the outer balancer ring has slipped. That could very well be the case and you'll be forever chasing your tail unless you do that FIRST. Everything with the timing is generated from TDC and if it's not right, you'll never find the trouble.
         
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        • AJ/FormS

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

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          I'm not telling you to degree the cam.
          Just making a suggestion as to why the tune has changed
          If you are 100% sure your dots were correctly indexed, in most cases that's gonna be close enough for maybe 90% of guys.
          What I am saying is if the last guy installed the cam at 8* advanced and yours came in at 0* advance, that is a huge difference.
          Does it matter?
          To intake manifold vacuum, yes. To cylinder pressure,yes. To absolute power,yes.These are numbers.
          To you, a streeter; not much.unless the cylinder pressure tanks. But the alloy heads took care of that. So yur good to go.

          Yur on the right track with proving the TDC mark, and with searching for a vacuum leak.

          BTW;
          I have an Eddy-headed 367 torque-monster. At one time, two decades ago now,lol,, I was running a Mopar 292/292/108 cam @11.3 Scr. That cam idled down to 600 in gear (manual trans), and pulled itself along on flat level hard surfaces, with 3.55s ........ at 5* Timing. Point being, when you get the fueling right, you will be able to idle that bad boy right down, using timing.

          Your low-speed fueling consists of
          fuel-level
          Transfer slots
          idle enricheners (mixture screws)
          airbleeds
          Idle-air bypass; aka the PCV, and secondary leakage around the butterflies..
          And in your case, it looks like a 4-corner idle system, so you gotta keep them cooking at the same time.

          Idle-timing does not matter. Don't get hung up on a number. You can idle that monster anywhere from 5 to 25 or even 30 degrees, it does not matter. What really matters is to get the transfer-slots and mixture screws playing nice together, and to get the off-idle tip-in to not hesitate or stumble. It starts with your transfer slot exposure, underneath the butterflies set to a lil taller than wide, and the mixture screws set in the middle of their adjustment range; then leaving them there, use timing to set the idle speed to whatever you want or need.
          If the fueling still ain't right, you need to add/subtract air thru the idle-air bypasses that are available to you. Or add/subtract fuel from the transfer slots in tiny increments. Always followed by adjusting the timing to control the idle-speed.
           
          Last edited: Sep 21, 2020
        • LovetheA's

          LovetheA's FABO Gold Member FABO Gold Member

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          Thank you Rusty and AJ/Forums and everyone else that chimed in with help and suggestions. I’ll start with finding true TDC and looking for vacuum leaks then by process of elimination go from there. I’ll keep my progress posted. Thanks to everyone as always.
          Carl
           
        • CRUZE 418

          CRUZE 418 FABO Gold Member FABO Gold Member

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          Now I have a question. Before I learned (and I am still learning) to degree a cam, I have always TDC #1, top gear dot at 6 o'clock, bottom gear at 12 o'clock. What is up with all of this top gear dot 12 o'clock , bottom gear at 12 o'clock, #6?
           
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