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Tri power tuning issues

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  • Norris W.
    Very Frequent User
    • December 1, 1982
    • 683

    Tri power tuning issues

    My '67 435 coupe runs like crap.

    It doesn't want to idle and hard to crank hot, despite the fact that the carbs were built by Holley's custom shop (then shelved dry for several years before running). We freshened the engine last year with pistons, camshaft, lifters, heads done, etc, etc. It runs about the same now as before.............. like crap. Oh yeah, trans ign. re installed in car after previous owner had substituted points/condensor for fix for dead ignition box, so ignition virtually eliminated.

    I'm putting a NEW in the box set of carbs on it that I've had in my parts stash for 10 yrs or better, but when pulling the carbs I noticed that the front two holes under the front carb are black and sooty. Side note: I've never cracked the secondaries since the motor has been back in the car, and it's been driven less than 50 miles.

    What does the blackness under the front carb mean. Compression seems about even on all cyls. One other thing, sometimes when hot, engine labors on starter, much like extremely high timing, with a loping cranking cycle that clears after several revolutions. This would almost seem to indicate fuel in a cyl, like maybe a leaking needle/seat, but replacing all 3 and resetting float levels with car running didn't do anything to help symptoms.

    Is it possible that some internal leak somewhere in the front carb is making it go real rich in some way that's not noticeable after cutting off and looking down in the throats? The plugs look VERY rich, but the way the car has been idled around and cranked and shut off a good bit foolin' with carbs, that's no surprise.

    Ironcially, this is a kind of situation that I'd probably try and venture some answers on if somebody else posted it, but this one has got me past my point of patience. I've done the carbs myself on my '69's several times over the years with never a similar issue.
  • Don W.
    Expired
    • September 30, 1997
    • 492

    #2
    Re: Tri power tuning issues

    I had a 69 427 tri-power back in 73/74. Even back then there were a lot issues. The engine heat can warp the areas where the carbs mount the intake manifold creating vacuum and fuel leaks. After working with a specialty performance shop back in the 70's; the final solution was to switch to a low profile aluminum intake with 4-barrel holley.

    Bottom line; tri-power takes a lot of skill and knowledge to get tuned and running smoothly.

    Comment

    • Norris W.
      Very Frequent User
      • December 1, 1982
      • 683

      #3
      Re: Tri power tuning issues

      Don, I've got several other tri power cars and this is the only one that's kicked me in the backside in spite of substained efforts. I put the three new out of the box Holleys on this afternoon and the primary is POURING from what appears to be the accelerator pump, so back off we come. I am REALLY beginning to believe there's a ghost in this car that just wants to rest in peace.

      This is the same car that I found the original engine in a race car, found & bought the car and reunited the two, then mysteriously somehow a shop rag turned up in the oil pan after the engine was build and installed and caused a spun bearing. (unbelievable carelessness on my part or disgruntled employee????............... I'll never know for sure) After the resulting second freshening the carbs are making me nuts, and these crazy issues with this car have been going on for a decade.

      Comment

      • Mark #28455

        #4
        accelerator pump?

        The acelerator pump circuit is seperate from the main and idle circuits, so they should not be an issue. However, the accelerator "squirter" nozzles are located LOWER than the carb fuel bowl vent, so if the needle and seat assembly is not sealing well, the fuel may run from the squirter. If the needle and seat is really leaking a lot, you'll see the fuel shoot up out of the vent tube. How do you check? Remove the sight plug on the side of the fuel bowl and if you are able to set the fuel level and NOT have it running over, then the needle and seat is not leaking significantly. If that's ok, then you should look at the adjustment of the accelerator pump arm. There should be a minimal amount of clearance between the accelerator pump arm and that crazy spring loaded nut/bolt deal. If there is no clearance at all, vibrations can be induced in the pump diaphragm which can sometimes pump fuel out the shooter.

        The other common causes of a rich running Holley carb are: If the primary throttle blades are open too far at idle, exposing more that about 0.030" of the off idle transfer slot. A blown power valve (or corroded/leaking power valve). Crap in the fuel line which then lodged in the needle and seat assembly - can be really frustrating as it can sometimes break loose and then lead to an intermittent problem. Corrosion on a brass needle and seat or cracking of the viton tipped needle and seat. That white corrosion that forms in the fuel bowl breaking loose and gumming up the seal on the power valve, etc.

        Mark

        Comment

        • Jim T.
          Expired
          • March 1, 1993
          • 5351

          #5
          Re: accelerator pump?

          Mark has mentioned what I was going to post about the power valve, if it is ruptured the car should run, but run best at the higher rpm when an unruptured power valve would be supplementing fuel. All it takes is a backfire on startup or slight stumble on take-off to rupture the power valve. Anytime that I had one rupture was verified by removing the the air cleaner lid, starting the engine, and putting a finger over the vertical fuel bowl vent. If my cars engine died immediately I replaced the power valve and fixed the problem. Have been taking care of my Holleys since 1974. One other problem I had recently with a Holley 4-barrel. The nylon float sunk because it became filled with fuel. Replaced both nylon floats with Holley metal ones.

          Comment

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