Slant Six Won't Rev over 3500 RPM

Slant 6 Engines

  1. armyofchuckness

    armyofchuckness The Flying Valiant

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    Well, the Flying Valiant is flying again, sort of. I've got it running and driving, and I've clocked a little over 600 miles on it sorting out bugs. We're trying to drive it from Gainesville, FL to Carlisle in five days, and while they engine has been running great, I can't for the life of me get it to rev above 3500 RPM. It acts like there's a stop in the engine and just sits at 3500 in first. Sometimes it will sputter and after a while it will buck and I'll back it down. Here's the specs:

    1964 Valiant, 1974 225 bored .060 over.
    Ported, polished head with the enginebldr valves, hardened seats, and .100" planed off the head.
    Offy 4bbl intake with Eddy 1403 500CFM set one stage lean on power and cruise modes, but it's been giving me trouble at just about any rod jet and spring combo I throw at it.
    Recurved electronic distributor
    Dual Dutra Duals
    Erson 280/270 cam
    HEI system with Mallory Promaster 29440 coil
    Stock fuel pump and filter on 5/16"

    We've tried just about every lean combo on the tuning chart. We couldn't get it above 3200 RPM initially, but we set the plunger to the lean setting and put the weakest springs in the carb and we were able to get it to creep up to 3500.

    I've adjusted the timing from everything form 10° advance to 30° advance, and that seems to make no difference. Vacuum advance on the car seems to have suction.

    I have an o2 sensor and gauge, but it's the Westach needle gauge and a one wire o2 sensor and it's all over the place. I think the sensor might be fouled because the car was running super rich at stock settings which is why we've stuck to lean testing. It still puts out a puff of black smoke on initial startup, but that goes away at idle and friends watching the car haven't seen any black smoke while I was driving it.

    Any ideas?
     
  2. rklein383

    rklein383 Well-Known Member

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    fuel delivery issue??? fuel filter maybe. Rod
     
  3. armyofchuckness

    armyofchuckness The Flying Valiant

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    Maybe. I'll check the pressure tonight. Brand new Napa 3002 filter. Nice and big.
     
  4. nm9stheham

    nm9stheham Well-Known Member

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    What do you have for mufflers? It sounds like either the fuel flow is restricted or the exhaust is restricted. Glass packs can be a problem in this regard it they deteriorate.

    Is the throttle opening fully from the pedal? Sounds too simple but.....

    Any chance that the cam was installed with the timing waay too advanced? It would be easy to check by looking at the valve positions versus crank timing.

    It will tell you something on AFR at WOT to:
    - Warm it up to full temp
    - Swap in a set of new plugs
    - Drive it at the 3500 RPM limit for 10-15 seconds
    - Cut ignition and stop and look at the plugs
    (The old-fashioned way AFR was tuned in the old days prior to O2 sensors....)
     
  5. whitepunkonnitro

    whitepunkonnitro Well-Known Member

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    Did you maybe skim over the basics...lash too tight?
     
  6. brian6pac

    brian6pac Well-Known Member

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    I'm thinking exhaust restriction, loosen the bolts at the pipe to the manifold and see if it is the same, easy and cheap and will rule out exhaust.
     
  7. jos51700

    jos51700 Well-Known Member

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    Add more boost or disconnect the brakes.
    3500 will seem plenty fast at that point.
     
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    • armyofchuckness

      armyofchuckness The Flying Valiant

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      Throttle opens all the way. The engine will rev higher in neutral. I got it up to 4500 before backing off. It won't do over 3500 in gear though.

      Cam was installed and degreed by Charlie Schmid, and if he checked it twice. There's probably very few people that have put in more Slant Six cams than Charlie.

      I have the dual dutra duals running to to a Y pipe that runs through a single 2.5" pipe to a cat-back style exhaust. It should have more than enough exhaust flow. The whole system is basically brand new. That's an intriguing suggestion though.

      Valve lash has been checked twice and is matched to the specs of the cam, so I really doubt it's that.

      Good food for thought though, guys. Thanks!
       
    • krazykuda

      krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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      You need to wind the rubber bands tighter...

      Power Band.jpg
       
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      • Mopar Tim

        Mopar Tim FABO Gold Member FABO Gold Member

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        I would still say there is a problem with the timing. Advanced too far. Just a guess, but makes sense. IMO:thumbsup:
         
      • armyofchuckness

        armyofchuckness The Flying Valiant

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        I thought so too, Tim, but it doesn't matter if I'm at 10, 20, or 30 degrees advance. It always stops right at 3500 unless it's in neutral, and then it revs higher.
         
      • brian6pac

        brian6pac Well-Known Member

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        O.K. disconnect the exhaust, I didn't know you had a cat. The rich exhaust (fuel) will burn in the cat pluging it up totally when running. Can you unbolt the cat from the head pipe?
         
      • armyofchuckness

        armyofchuckness The Flying Valiant

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        There's not a converter. It's a cat-back style muffler, but there's no catalytic converter in the line. It's basically Bassani's version of a Flowmaster.
         
      • sccachallenger

        sccachallenger Well-Known Member

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        How does it "feel" when it hit its limit?
        Have you checked float setting and fuel pressure?
        Throw in the richest rods or jets that you have to eliminate a too lean condition.
         
      • nm9stheham

        nm9stheham Well-Known Member

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        Yes, Charlie should know..... I'd still check it by looking at the #1 and #6 valves with the timing mark at 0. One of those 2 cylinders should have the 2 valve open almost equally, with the exhaust closing and the intake opening. And make sure to recheck the mark on the pulley being at 0 with #1 truly at TDC. This is such definite problem that nothing should be neglected.

        Is this one of the Bassani mufflers that take a fiberglass packing? If so, I wonder if this is exceeding the flow limit or the glass has come loose. Beyond the exhaust, is the bowl vent open? What is the setup for the fuel lines and tank? Fuel pressure sure would be a good thing to monitor.
         
      • Pascamp

        Pascamp Well-Known Member

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        Sounds like a bad fuel pump to me. Even brand new ones fail. Wrong spring installed, diaphragm not operating properly from sitting in a warehouse for years, ect. The pump will basically go into valve float (cavitation)at a certain rpm, and that's it...no more fuel. When you're engine is in neutral there's no load and requires less fuel. If you've got another one laying around swap it on to rule it out. The adjustments you made to the carb and the results you got also support this.

        I think you can rule out ignition. There would be a bunch of other symptoms. Valve lash would be heat related not rpm, and I would expect some backfiring, glowing manifolds, or other hoopla. Exhaust is possible and easy to rule out. I'm definitely leaning towards a fuel supply problem. Fuel pump, regulator, carb, ect. Sometimes it's easier (and faster) to swap on known parts than to play forensic pathologist.
         
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        • Deemo

          Deemo Well-Known Member

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          If it was exhaust you can take a laser temp gauge and check the temp??
           
        • nm9stheham

          nm9stheham Well-Known Member

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          Hmmmm..... What temp or temp change would you look for as being good/bad?
           
        • armyofchuckness

          armyofchuckness The Flying Valiant

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          It was the ignition module! I replaced the "value brand" module I had in there with a Flamethrower HEI module and now the car will rev as far as I care to take it! Thanks all for the advice. Lots of good stuff for me to think about for other applications. Hope this post helps out other folks that are having this problem with their cars.
           
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          • Thanks! Thanks! x 1
          • KosmicKuda

            KosmicKuda FABO Gold Member FABO Gold Member

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            Hey that's awesome. I'm driving my 64 225 Val to Carlisle so it sounds like you'll be going after all. What color and body style is yours?

            Oh, and you should buy the parts SSD recommends.
             
          • armyofchuckness

            armyofchuckness The Flying Valiant

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            Very cool! Mine is a 64 V100 two door. It's bright blue. You can see other pics of my car over on my Instagram. I took this one yesterday.

             
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            • nm9stheham

              nm9stheham Well-Known Member

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              'Value brand'..... LOL. That is a new cause but you never know. Glad you got it solved.
               
            • AJ/FormS

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

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              I was just gonna say that! Cheap-azz module I mean.lol
              Actually no; I had some other questions but ,I guess I'm late to the party.
               
            • KosmicKuda

              KosmicKuda FABO Gold Member FABO Gold Member

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              I had issues with mine that I won't go into here but I was worried I couldn't get it fixed in time. But as of 8 PM last night, it's a go. Keeping my fingers crossed though that Mr. Murphy doesn't show up again.
               
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              • pishta

                pishta I know I'm right....

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                'Value brand'.. rev limited to save gas too! Some of those ECU's have fake TO-3 transistor bodies glued to the top and use cheaper TO-220 through hole mount versions inside. Take it apart and show us whats inside.
                 
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