Paxtoned 416 won t fire with lid on when engine is cool

Discussion in 'Forced Induction Mopar' started by evil 340, Aug 30, 2018.

  1. evil 340

    evil 340 Well-Known Member

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    k this is my first supercharged engine and trying to work a bug out.
    416 stroker motor
    Mr norms Paxton sn60 setup.
    Stock 72 340 manifold and 800cfm thermoquad ( I know maybe underkill for everything else it’s got but it s all there to accept the vintage mr norms Paxton setup)
    Full msd ignition system.
    Holley 12-920 fuel pump with boost referenced regulator
    Plenty of fuel and spark
    It will not fire with the clamshell on top of the carb (or carb box) sealed up. ONLY WHEN IT SITS LONG ENOUGH FOR COOL DOWN a.k.a overnight
    It will instantly fire tho when you remove the lid. And will fire right back up when it’s warmed up. Any suggestions would be great. Thanks in advance.
     
  2. evil 340

    evil 340 Well-Known Member

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    A pic

    1BF217DD-02D2-401D-AE07-EDEBC830EE3F.jpeg
     
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    • evil 340

      evil 340 Well-Known Member

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      Initially had a mechanical carter on it and it did the same thing. Went to a strong electric pump to get more fuel to it. The regulator is set at 12 psi right now. But I just got it on and plumbed so haven t fired it back up yet
       
    • brian6pac

      brian6pac Well-Known Member

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      I would say it's to rich or restricked in the intake (before the carb) when cranking with the lid it sucking fuel it doesn't need, pull the lid and get fresh air it fires. It fires cold because it needs the extra fuel to start cold.
       
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      • chargd72

        chargd72 Well-Known Member

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        Sorry for the sidetrack but just curious. Will that blower feed a 416? I thought they maxed out at 7psi on around 300 cid engines.
         
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        • mbaird

          mbaird mbaird FABO Gold Member

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          try squirting a bit of starter fluid or gas in then put the lid back on and try starting it.
          it might be the accelerator pump shrinking or expanding from the heat. I dont know blow thru carbs well enough to say for sure.
           
        • evil 340

          evil 340 Well-Known Member

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          Well it’s not an actual blow thru carb. Just a factory intake and carb. The norms box was set up just for the carb that’s on it so it would be kinda difficult to fit a different carb inside the box. The engine was run for a short while before the blower went on. The blower did make a minimal improvement but it’s more there for looks then anything.
           
        • chargd72

          chargd72 Well-Known Member

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          Did you try removing the charge pipe but keeping the box enclosed to start it? I wonder if there is some sort of restriction with the blower at low RPM.
           
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          • mbaird

            mbaird mbaird FABO Gold Member

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            maybe you should get a blow thru carb then up the boost.

            That would be one wild ride !
             
          • brian6pac

            brian6pac Well-Known Member

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            Not much difference in a blow through than a naturally aspirated one
             
          • evil 340

            evil 340 Well-Known Member

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            I will try removing the hose from the bonnet but I doubt it will help.
             
          • HemiSSDart

            HemiSSDart Dartus Interuptus

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            I've had a bit of experience with these. How do you start it? Pump once, repeatedly, or not at all? It is my experience that they are way rich when cold. Do you have stock floats in the carb? Norm had to have specially made floats, but they were because of the pressure and would collapse. I doubt it has anything to do with starting. Any other symptoms when warm and running? Stock Paxton air cleaner and hose?
             
          • evil 340

            evil 340 Well-Known Member

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            Aftermarket hi flo filter but the rest is norms stuff. I have the floats that came with the kit. But th carb already has the newer style uncrushables in it.
            As far as the way i start it i have tried to start no pumps. 1 pump. A couple. It has almost popped on a couple occasions but never saved it. I just got the pump in today and got it ready to fire but it wouldn t start with the box sealed. I didn t wanna pull the lid cause i had gas all over my hands and was running out of time for the day. I m gonna try tomorrow and see how it acts with this new pump and reg

            Thanks to everyone with your suggestions. I m hoping its something stupid i have overlooked but i want to get this figured out before too long. I just got it back from the guy who built the engine and he wanted to address the pump first so i am. Just figured i d throw this out there before i dive head first into it
             
          • famous bob

            famous bob mopar misfit

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            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
             
          • 67Dart273

            67Dart273 Well-Known Member

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            I think you are getting fuel perk/ siphon when sitting. Or else NO fuel in the morning.

            Is the fuel tank for certain vented? If the carbon can/ evap system has been removed/ changed, the vent system is suspect.

            What are you running for a pump, electric or mechanical? If it's not electric, try to determine if the fuel is pulling back over night. Pull the lid before cranking, pump the throttle, and see if you have fuel immediately from the accel pump
             
          • chargd72

            chargd72 Well-Known Member

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            Is your timing locked out? What is it set at?
             
          • evil 340

            evil 340 Well-Known Member

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            I was wondering possible timing as well.

            The tank is vented all the way to the original emissions canister.
             
          • AJ/FormS

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

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            IDK anything about this set-up, but I do know that in order for the fuel to come out of the fuel circuits, there has to be more pressure in the bowl than at the butterfly. So I'm wondering if your throttle valves are open too far and the cranking is pulling air around the throttle valve with no fuel being delivered to the transfer ports.If you have a working choke and fast idle system this might not apply. But it remains that the float-bowl vent has to see at least atmospheric pressure at start-up.

            Usually the PCV is the idle-air bypass, so you can close the throttles more. With a super, IDK how you would run a PCV. And if you end up not running one,then for sure your T-port sync will be off, and very likely the butterflies will be open too far.
            Try closing your speed screw a couple of turns and see if it likes that. If yes, then you will have to figure out how to make it idle lol.
            You might need what they call, a throttle kicker.
             
          • chargd72

            chargd72 Well-Known Member

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            My timing is locked out at 36* but I retard 10* during startup. If I disable this feature, it's more difficult to get started.
             
          • Turbo poly

            Turbo poly Oz Charger

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            Hi Evil 340
            My car does a similar thing , it was worse with my Holleys , one a 500 2bbl I converted to Blowthrough and my C and S 650 , and to a lesser extent my Thermoquad , however it did not suffer as bad when I use avgas , we have garbage fuel in Australia now , 91/98 and it has 5-10% ethanol which has a low boiling point , and after hot shut downs floods the crap out of the engine very bad with the metal carbs , if i remove the carb bonnet it is not an issue , I ended up putting insulating spacers under the carb instead of a aluminum ones this helps too . Good luck :)
             
          • evil 340

            evil 340 Well-Known Member

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            Ok. So. The problem I believe is solved almost. The engine builder said he was having issues with the factory choke working properly due to the aluminum heads with no heat riser holes. He said he disconnected the rod at the carb. But the rod got wedged in all that linkage and was not letting things move properly. I freed this and for the past 2 days it starts cold. Pretty easily. I honestly think the electric pump helped as well. Thank you all for your suggestions and help.

            So now I’m having a new problem. The car seems to idle ok but when you take it for a ride it breaks up pretty bad. As soon as you give it some throttle it breaks up. Timing or air fuel mixture? Because it ran fine before the blower install.

            I m not a mechanic. But I m not afraid to do whatever I have to to make it work and not burn it to the ground lol
             
          • evil 340

            evil 340 Well-Known Member

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            Again I appreciate any suggestions
             
          • brian6pac

            brian6pac Well-Known Member

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