Miss and carb tuning troubleshooting

Small Block Mopar Engine

  1. alindeman1989

    alindeman1989 Well-Known Member

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    Hey all, I have been reading thread after thread trying to narrow down some of the issues I have and took in a bit too much information and need some help to get me in the right direction before I start tearing it apart this weekend so I'll lay out the problems at hand.

    73 Scamp specs:
    -318
    -eddy performer intake
    -eddy 1406 carb
    -long tube headers
    -2.5 in exhaust
    -Trailbeast's HEI and distrubutor
    -NGK BKR6E spark plugs
    -possibly some unknown rv cam, has a slight lope at idle
    -initial distributor timing set at 15 btdc, total 35 @2500rpm, vac advance can set at +15

    So I'll start out with the miss, at idle, part throttle acceleration, and wot there is no apparent miss at all, but at cruise in town/freeway or free revving the motor up past idle at a constant rpm, there is an audible "pop" coming out of the passenger side exhaust. Has anyone experienced a similar issue? Leaking intake manifold gasket? Burnt valve? Not sure.

    *Edit* Also, if i get on it pretty hard, and let off the throttle to coast, the back firing becomes more apparent, if that helps at all.

    And the other thing I am dealing with is how the carb is running. Currently set at 1 stage richer in cruise (to see if that would get rid of the miss) and using the silver springs, going to go lower to possibly see if helps the issue. I have been monitoring on my wideband this past week on my commute to work, idle afr is at about 15-16, cruising about the same under 35 mph, but as soon as the rpm's go a bit higher cruising at 60-65 mph, afr is at about 14-14.5 (which is what I want below 35 haha). Springs might have something to do with this, thinking not having enough manifold vacuum at 2500 rpm cruising on the freeway to keep the rods down? I was under the impression the afr shouldn't change much if the rods are down at cruise even at a higher rpm, if that's the case, change the rods cruise mode one stage more rich and softer spring to balance it out no? And the final issue I have is lightly tipping into the throttle to accelerate, afr is around 14's, but any sort of not so light movement to get up to speed/half throttle/wot the carb just dumps fuel, afr hitting 10-11. Stock fuel pump (fairly new replacement) pressure sending too much gas to the carb? Float adjustment? I don't know, but will reset everything this weekend. Every post I have seen about issues with this carb seem to be off idle stumble or lean bog conditions when flooring it at speed, I have the complete opposite of this issue and she gets up an will spin the tires off as soon as I peg the gas.

    So those are my woes, I have on the way a rebuild kit for the eddy, a fuel pressure regulator to limit the fuel to carb to about 5 psi as per spec, 1/2" wood carb spacer because sometimes is takes a sec to start when hot, (shit california gas evaporates too easily). I gave my input on the things that I think might work and what the issues could be and you guys will probably school me about HAH! Hopefully I'll get something out of it, I get the basic concepts and all and am having a fun time learning, tuning, and seeing what others have done in their experience.
     
    Last edited: Apr 26, 2017
  2. rustycowll69

    rustycowll69 Well-Known Member

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    compression test? leak down test? plug reading?
    I like the spacer idea. I like the carb kit, because the needle and seat may be leaking, especially when hot. Immediately after hot shut down, look down the primaries. Do you see any wisps of smoke rising up, or a fog of vaporized fuel. That usually means worn needle and seat, and/or too high float level.
     
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    • swies

      swies Wish I had more time.

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    • alindeman1989

      alindeman1989 Well-Known Member

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      Compression test is due this weekend and will probably tell me a lot haha. Will probably get a leakdown test kit when I am at the parts store too as I have been meaning to get one for a long while and have a compressor now. Plugs, last time I checked had black carbon around the ring, spanned down about 2 threads, porcelain was somewhat white with light black tinge from what I remember, no idea as of now, but same symptoms then. I'll pull the filter off and check out for smoke when I get home from work while its hot and report back. Thanks!

      P.S. Working on cars at an apartment with no lighting in the dark sucks, needa find a new place with a garage!
       
    • seabee

      seabee FABO Gold Member FABO Gold Member

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      Have you put a vac gauge on it?
       
    • alindeman1989

      alindeman1989 Well-Known Member

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      Last time I checked, at idle it was pulling about 18-19" Haven't tried seeing what it does while driving though, might be a good idea, thanks.
       
    • AJ/FormS

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

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      Q1,Are your exhaust pipes shared between sides?

      I'm going with a bad header-flange gasket on the side that pops.
      At closed throttle decelleration, the headers will pull a vacuum at the flange, and if the AFR is rich,or the ignition timing is late,the still burning gas mixes with the fresh air being sucked in by the header, and explodes, causing a pop in the pipe. If the exhaust was dropped you would probably see flames coming out of the collector.
      This is more apparent under compression braking as the engine draws excessive amounts of fuel past the not-quite-closed-enough throttles.So that leads to the question,
      Q2) what is your idle speed? and Q3) have you synced up your Transfer ports?What Champion heat range does your plug crossover to? I run Champion RN12YCs, IIRC, 12s are fairly cool. Your engine might like 9s.
      So to recap; get your T-port synced up, hoping to set the idle closer to 650/700 in Neutral, Put the carb back to stock,and fix the header-flange leak. If you have an IR gun, you might be able to prove the leak. It will be the tube that runs the hottest about 2 to 3 inches from the flange. It will be at least 100 to 300 degrees hotter than the others. It runs hotter cuz the gas is burning in the pipe.
      Good luck.
      BTW
      Once the T-port sync is established, do not mess with the speed screw! Don't be surprised if it takes less initial timing to slow the engine down. 15* is, IMO, too much for a cam that idles at 18/19 inches. I think 10 or 12 will be better. Getting the transfers synced at idle is job #1.
      For help with this click on the little blue M below, or go visit the Holley site.

      Also,IMO 35* at 2500 is too much . But if it doesn't detonate then I guess you are alright. I just know that I would not run that much. Then again,I run 87E10, in my 10.9compression 367cuber.
      Q4) What stall are you running?
       
      Last edited: Apr 26, 2017
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      • rustycowll69

        rustycowll69 Well-Known Member

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        is the needle steady? you say 18 to 19", but at what idle rpm?
        I agree with the suggestion to look for an exhaust leak, that could be a source of the popping noise.
         
      • alindeman1989

        alindeman1989 Well-Known Member

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        A1) They are shared, has an h-pipe placed in about 12 inches from the collector flange. You know, you might be right, I don't recall a miss on that side before I put headers on (Dougs), that or it wasn't audible enough to hear with the old quiet exhaust and I didn't notice. There is no leaks I can hear of, but I'll pick up a cheap IR gun at harbor freight to check.

        A2) Idle speed is set at 950, in gear about 650.

        A3) As far as I know they haven't been synced by the last owner and I have not done so myself, but I will most definitely read up about it and follow your write up. NGK BKR6Es are the equivalent of Champion RN9YCs, so I think I am good there.

        Once the T-port is synced I'll check timing and see what she ends up liking better, and I might be getting away with 35 because I throw Chevron 91 in all of my rigs, Cali gas is piss water with all the junk they put in it lol.

        A4) Stall is at about 2000 rpm, stock as far as I know.

        Really appreciate the response, as this is a great starting point for sure, thanks. I wanna tear it apart right now, but damn I have to wait for the weekend.

        Needle doesn't move at all at my 950 rpm idle, have to give her a good rev for them to come up at all, in gear I am not sure though as I don't have another head to stay on the brakes while I check. And I hope it's that simple, it's pretty damn loud when I hold the rpm up steady in park vrrmmmmmmmm POP vrmmmmmmmmmm POP vrrrrmmmm POP POP, pretty inconsistent.

        No smokey here when I checked right after got home from stop and go traffic.
         
        Last edited: Apr 26, 2017
      • RustyRatRod

        RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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        Have you tuned the carburetor to the engine? And I mean TUNED, not adjusted. BIG difference.

        The 1406 is an economy carburetor and is likely too lean for your combo.
         
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        • alindeman1989

          alindeman1989 Well-Known Member

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          Tuned? I don't think I would have gotten a 1406, but it's what the car had when I bought it so I figured I'd try to make the best of it as half the people I have read say it works great for a mild 318 and the other half say it always has issues, like my dad, said throw it in the trash and get a holley, problem solved lol..
           
          Last edited: Apr 27, 2017
        • AJ/FormS

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

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          Comments inside the quote
           
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          • alindeman1989

            alindeman1989 Well-Known Member

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            A5) Yes, it has a functioning PCV valve, a little noisy though, but I have replaced it 2 times and still the same. Hose isn't collapsed either.

            A6) No, tdc mark has not been proven, could explain how the car is running how it is if the damper has slipped.

            A7) Mixture screws still work fine. Turning in leans idle afr, turning out richens.

            A8) Secondaries seem to be fully closed, will confirm later today.

            A9) Compression and leak down test will be done this weekend. I'll post the results. Thanks again.

            *Edit* Cold start idle at 950 and only drops to 800 in gear while brake is applied, warm same 'ol 650.
             
            Last edited: Apr 27, 2017
          • AJ/FormS

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

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            Comments in the Quote
             
          • alindeman1989

            alindeman1989 Well-Known Member

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            A5) Vacuum gauge is fairly new, so I would possibly think it is. It's intermitent, at idle sometimes it's quiet, usually at cold start, when warm it does make more noise at cruise.

            A10) yes, it will stall.

            As for curb idle in neutral is 950, in gear, warmed up, brakes applied is 650. Will double check to confirm on my next reply.
             
            Last edited: Apr 27, 2017
          • AJ/FormS

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

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            Last edited: Apr 27, 2017
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            • alindeman1989

              alindeman1989 Well-Known Member

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              Haha, the car is pretty loud, it's the certain rpms where it doesn't drone that I can hear it.

              As for the stall, it does stall at 2000 rpm when I gas the car with the brakes applied, I was just saying that's what I have seen is stock for a factory 318?

              Curb idle, yes, 950 rpm on a warm motor, choke confirmed all the way open, 650 once it's dropped in gear. It's been a while since I did the idle, but I remember that's what it ended up being when I set it as per Edelbrock's instructions on setting idle mixture. But I have a feeling if it is reset lower, the car might stall if I put it in gear if curb idle is at 750. Should I try and see? or just leave it as is for now until I rebuild the carb and set it this weekend. Following your T-port guide, what do I go abouts for the idle mix screws?

              PCV, hmm, it's tapped off the rear center port on the carb as how it was when I got the car, but there is another port on the front that is the same diameter. Vacuum can is tapped of the spark port on the front lower left of the carb.
               
            • rustycowll69

              rustycowll69 Well-Known Member

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              that's where the vacuum port for dist. vacuum advance is on the Carter TQ, so that's probably the same on the edelbrock.
              As far as the idle speed, 950 seems a little high. The higher the idle speed, the higher the vacuum, so it can be a little misleading on the amount of idle vacuum. But a non stock cam can force you to raise the idle speed to smooth out the idle. How many turns out from seated are the idle mixture screws?
               
            • alindeman1989

              alindeman1989 Well-Known Member

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              Not sure how many turns out, but I'll let ya know when I am near my car again.
               
            • mderoy340

              mderoy340 Well-Known Member

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              I have been monitoring on my wideband this past week on my commute to work, idle afr is at about 15-16, cruising about the same under 35 mph,

              You are way to lean.
               
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              • alindeman1989

                alindeman1989 Well-Known Member

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                That I know, going up the next rod size makes it too rich, 12-13s at cruise and even worse on power than it already is, usually try to aim for 14s cruise/idle in gear. Don't want to keep throwing stuff at it til I rebuild the carb this weekend, reset the floats, and set everything back to stock and go from there. Also have to find out what my compression is and where true tdc is on my damper, can't wait that's for sure.
                 
              • alindeman1989

                alindeman1989 Well-Known Member

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                Idle mixture screws are out 1 7/8 turns.
                 
                Last edited: Apr 27, 2017
              • rustycowll69

                rustycowll69 Well-Known Member

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                starting position is 1-1/2 turns out, so as far as that goes you're pretty close to recommended.
                 
              • AJ/FormS

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

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                As always, comments inside the quote
                 
                Last edited: Apr 27, 2017
              • alindeman1989

                alindeman1989 Well-Known Member

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                Alrighty, TDC first and then I'll follow along from your notes as well as keeping a spreadsheet of what is done to the carb.

                Well shit... Guess we will find out when I get back from work, I'll swap it over before I leave. God I'll feel dumb if it was something that simple, shouldn't have expected it with how out of wack everything was set up when I got the car, no mopar linkage adapter, 2 BBL throttle cable bracket, kick down not set right, throttle only opening about 1/4 the way, vac advance on wrong port, among other things I had to fix, but I didn't think to check the PCV routing.

                Yes, timed vac port, no vacuum at idle.

                Man, thanks so much, you don't know how much I appreciate it, I'll get back to ya'll tonight.
                 
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