Carburetor trouble

Discussion in 'Fuel and Air Systems' started by Don Bagwell, May 9, 2018.

  1. Don Bagwell

    Don Bagwell Member

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    I have a quick fuel 950 on a 630 hp 360 stroked to 423 running down the road at 80 it performs well start punching it up to and above 100 mph and it starts loading up on me and makes my fuel pressure go crazy any help would be appreciated
     
  2. roccodart440

    roccodart440 Well-Known Member

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    What do you mean by fuel pressure goes crazy? If it's loading up under WOT I'd double check your timing and check rear jet size.
     
  3. j par

    j par Well-hung Member

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    Welcome to the forum.
    You come to me on the day of my daughter's wedding and you want me to do you favors and yet you haven't even offered me a cup of coffee !?? LOL
     
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    • j par

      j par Well-hung Member

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      Maybe your fuel pump is not regulating the pressure well and at high speed is Conjuring 2 much?
       
    • Murray

      Murray Well-Known Member

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      Your coffee is here waiting for you.
       
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      • j par

        j par Well-hung Member

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        Then take a left turn at Kmart.....
         
      • brian6pac

        brian6pac Well-Known Member

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        What RPM, what vacuum, what fuel pressure, secondary's open 1/2 way all the way? The more info the better.
         
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        • Don Bagwell

          Don Bagwell Member

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          Fuel pressure consistently runs at five pounds in town and on short runs once I start accelerating hard on long runs the fuel pressure starts bouncing between 0 and 3 until something like the carburetor loading up and choking out and I smell gas then the fuel pressure goes back to 5 this continues to happen until I stop for a couple of hours then it’s back to normal with no problems
           
        • Don Bagwell

          Don Bagwell Member

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          Also I have a crank trigger with the distributor locked out, I’ve tried different fuel pumps still the same I think it lies in the carburetor
           
        • brian6pac

          brian6pac Well-Known Member

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          Do you have a PV on the secondary's? is the pressure drop consistent with RPM, what RPM does this happen, What size fuel line do you have? filter plugged up? filter in tank? Electric pump in the rear? mechanical pump? A lot of things can cause pressure drop but not normally carb.
           
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          • Don Bagwell

            Don Bagwell Member

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            PV on secondaries yes, pressure drop consistent with rpm no,eyes on the road not on tach,3/8 fuel lines, I’m going to say no filter plugged up only three thousand miles on everything from fuel tank threw the motor, electric pump in rear, fuel will at some point actually squirt up into the air filter
             
          • j par

            j par Well-hung Member

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            Almost sounds like the float needle sticking? Like it goes all the way down and then all the sudden the float drops and the gas comes rushing in and maybe can't get close and time to overspill? And then get stuck up until it empties and starts sucking dry and drops open again? Just spitballing....
             
          • brian6pac

            brian6pac Well-Known Member

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            I'm sure it has baffles in the bowl? sound like float hanging for sure, needle open pressure drops and fuel overflows. That thing would have to flow a lot of fuel to drop the pressure to 0 or 3 psi,
            what is the gph on the pump.
             
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            • Don Bagwell

              Don Bagwell Member

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              100 gph
               
            • roccodart440

              roccodart440 Well-Known Member

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              YOur fuel pressure should not be dropping like that under load, definitely not down to 0-3psi.

              When you say loading up, smelling fuel, I have to wonder what the afr is and also what the plugs look like.

              I'd like to see you strap that thing to a chassis dyno and see what its doing under a controlled environment.
               
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              • Mattax

                Mattax Just the facts, ma'am FABO Gold Member

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                Description sounds like vapor lock. If it is, it may be occuring on the suction side and that's why the pressure drops and then burps up. You smell fuel because its coming of the carb as all vapor instead of mostly a dispersed liquid. At moderate throttle the engine acts something like a combo of its too lean for the load and running out of fuel.

                Go over the entire fuel line. Look for any possible pin hole leaks on the supply side to the pump. Look for all locations that may transfer heat from exhaust and headers etc. Insulate as needed.

                I've added insulated firesleeve and then covered that with reflective type insulations since having a problem last April. I'd run the car the previous summer no problems at all. So sometimes all that's needed is summer fuel. I just preferred to take the extra precautions against very warm days in the Spring.

                This is the worst time of year for using pump fuel. Temperatures are often into 70s and 80s but we're still using winter fuel. Winter fuels are allowed much higher Reid Vapor Pressures (RVP). This helps cold weather starting, and is also cheaper to manufacturer. In our favor, every retail outlet must be be selling 100% summer fuel by June 1. Refiners and distributors must be supplying it by May 1. A few states also have fuel drivability requirements, and others have lower RVPs than the US EPA allows. So not all fuel across the US and Canada is the same.
                 
                Last edited: May 10, 2018