Too much pressure??

Small Block Mopar Engine

  1. PistolGrip

    PistolGrip Well-Known Member

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    I'm trying to bring a recently-purchased sleeping 273 back to life after it's been sitting idle for about 15 years. It's a 1965 180 HP with a newly rebuilt Carter 1781 2 bbl carb. After doing all of the other prep (oil, etc), the time came to try to start it. I began by trying a little starting fluid & after a little cranking, it STARTED!....It ran for a couple of seconds until the starting fluid ran out. I then hooked up the fuel line, expecting success. No such luck. I discovered the fuel pump was not delivering any gas, so I replaced it with a new over-the-counter pump for this car (the brand escapes me) & gave it another go. This time it started, but I got the "KILL IT" signal from the guy watching the engine - there was gas coming through the top of the bowl of the carb above the floats (accelerator pump?) and the base. I've tried a few adjustments, including a new needle & seat & gasket but the problem continues whenever I have the fuel line hooked up. Clearly(?) I'm getting too much gas & the new needle & seat aren't doing their job to stop the flow when the floats reach the highest point - about 1/4 inch from the top of the bowl. I tested the fuel pump pressure (while cranking - remember it won't keep running with the fuel line connected). The fuel pump pressure reads 7.5. The specs I see for this engine range from 5-7. Would that extra 1/2 lb of pressure make enough difference to cause my problem?...or what am I doing wrong? Would a fuel pressure regulator/gauge be the most reasonable cure? I feel like I'm really close, but......
     
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    • Murray

      Murray FABO Gold Member FABO Gold Member

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      I would be more inclined to blame the carb. I would consider a rebuild with a new needle and seat. Look in the bottom of the bowl- is there a lot of sediment? Maybe a new fuel filter is needed?
       
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      • nm9stheham

        nm9stheham Well-Known Member

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        Are you sure you set the float right? 1/4" or 5/16" is right for the BBD per my 65 FSM.

        The float could well be ruined and filling with gas and so not working with the needle & seat nor regulating fuel level properly. IMHO, a complete rebuild WITH new float is mandatory for a carb sitting this long and being this old. The gaskets will all be dried out.
         
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        • AJ/FormS

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

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          7psi is about the max a factory type 340 pump can put out, dead-headed.
          A teener pump is usually closer to 5.5, also dead-headed..
          I would think that if you have that much pressure,the float-valve is closing. I'm guessing the float is just set too high. But, IDK if the "installed" float valve can take 7psi. I know, that back in the day, they could. It could even be that the float is not properly held down with it's horseshoe-spring.
           
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          • toolmanmike

            toolmanmike FABO Staff Staff Member FABO Gold Member

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            New fuel pumps are garbage. A friend got 11# out of a stock replacement pump. A pressure regulator made his 440 run sweet set at 4#.
             
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            • Mattax

              Mattax Just the facts, ma'am FABO Gold Member

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              Was your pressure test done with the gage plugged direct in or on a tee?
              On a tee I, think 7.5 is too high for cranking test.
              If deadheaded, its high but might be OK. I'd still swap it out for one that has the correct max pressure over installing a regulator.
              Then see about getting a new diaphram and valves put in the old one (which has the correct spring in it).

              From the picture of one I found online, yes the 1781 has the accelerator pump's linkage through the bowl cover.
              Definately recheck the float and the needle and seat.
              Sometimes floats take on fluid. shock-gif.gif
              Try also setting the float at the low end of the spec, and if there are dry vs. wet specs for the carb, make sure your setting on the appropriate one.
               
              Last edited: Mar 15, 2019
            • PistolGrip

              PistolGrip Well-Known Member

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              The carb has not been run since the rebuild & everything was gone over by a local professional 'old carb guy'. The pressure test was done on the rubber fuel line where I removed the fuel filter....no tee. I guess I could try lowering the float.....

              Carter Carb.jpg

              Fuel Pressure reading.jpg
               
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              • 3406pk

                3406pk Well-Known Member

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                I had similar prob with another carb. Finally found the float had leak and was full of gas. Would not raise up the needle to shut off.
                 
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                • nm9stheham

                  nm9stheham Well-Known Member

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                  Ask that guy if he replaced the float with a new one; I am not sure what 'gone over' means exactly. A float leaking or getting 'gas-logged' is not always readily visible. I have had them look fine in a close visual inspection but yet still absorb gas and flood the carb. Looks like BBD floats are still available, with just a quick look online.

                  Trying the regulator may be easier... it just seems that 1/2 psi would not typically be a problem. Your gauge looks like a reasonably accurate one.
                   
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                  • toolmanmike

                    toolmanmike FABO Staff Staff Member FABO Gold Member

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                    Exactly I would put the regulator on and adjust it to 4# and see what works. Leave it on. You don't need 7# of pressure. It will just cause problems.
                     
                  • MOPAROFFICIAL

                    MOPAROFFICIAL Well-Known Member

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                    Just rebuild the carburetor the needle and seat is shot it won't seal there for the bowl just fills up and overflows out the main Wells and down into the carburetor and out everywhere else. Also throw some 91 in the tank, fuel stabilizer , if the gas is old.
                     
                  • MOPAROFFICIAL

                    MOPAROFFICIAL Well-Known Member

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                    If you rev it, the psi will drop... after driving it will settling around/near 4psi.

                    The 'stock pumps' are high like that at 1st start.
                     
                    Last edited: Mar 17, 2019
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                    • TrailBeast

                      TrailBeast Slightly Twisted Member

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                      1. Needle/seat issues including junk in it not letting it seat.
                      2. Float leak or mis-adjustment
                      3. Pump Pressure

                      That's really all there is, but since lots of carbs run 7.5 lbs I would highly suspect one or even both of the first two.
                      I have that exact same carb on the Wife's 72 Dart and it runs 7.5 lbs without any problem.
                       
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                      • PistolGrip

                        PistolGrip Well-Known Member

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                        I took the carb apart again & discovered the little inverted "U"shaped spring that holds the float where it pivots was hanging up on the float in mid-range whenever gas was introduced into the bowl. I messed with it some & put the "U"shaped spring back so the float now moves freely. I even had some fun testing it to see if my repair would cure the problem. I was smoking a cigar & blew smoke into the fuel line with the empty carb right side up (float at the bottom of the bowl) & smoke flowed freely into the carb & out the little bowl vent. Then I did the same thing, gradually turning the carb upside down while again slowly blowing smoke & I could feel the smoke flowing less until it was blocked completely when the float reached the top of the bowl. I'm easily amused.
                        The carb works great now & no leak anywhere. Thanks for all of your help!
                         
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                        • AJ/FormS

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

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                          BadaBoom!
                           
                        • Murray

                          Murray FABO Gold Member FABO Gold Member

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                          A new way to test carbs. I am going to take up smoking.
                           
                        • stixx

                          stixx FABO Gold Member FABO Gold Member

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                          Don't. :)
                           
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                          • AJ/FormS

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

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                            Hopefully you are jesting.
                            The autopsy showed that Smoking contributed to the death of my mother, at age 60. The thing is, she never smoked in her life.
                            But she was married to an avid smoker; Who just happened to live to age 83. And to be fair, he died of an infection he contracted in the hospital from a simple operation. We did not do an autopsy on him to see what his lungs looked like from being a smoker for 70 plus years. He beat himself up pretty bad over losing his wife so young.
                             
                            Last edited: Mar 18, 2019
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