Improving acceleration using 2bbl Carburetor?

Slant 6 Engines

  1. chinze57

    chinze57 Push Button tranny and a Slant 6 that'll never die FABO Gold Member

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    When I first got my ‘64 Dart, I had my mechanic rebuild and tune my carburetor as initially it required constant throttle so as not to stall.

    That issue is slightly better now. When cold, it requires light throttle not to stall, when warm is 60/40 whether or not it’s needed. However, hot or cold, sometimes when going from a stop to partial or full throttle, it misses and sometimes stalls out.

    Then there’s the issue that there’s slow acceleration. Any decent acceleration requires full throttle.

    I’m curious if the issue of acceleration can be fixed with a 2bbl carburetor, as I’m not looking to do a full 4bbl conversion. I believe it should give me a bit more power which should help with acceleration. I also thinking that starting with a new (or newer) carb will also help me when getting it tuned, as it would be less likely there would be other issues with the carb.

    What causes the missing when I accelerate? Is it a fuel pressure issue, and if so, what’s a solution to that?
     
  2. George Jets

    George Jets 1967 Dart 2 Door FABO Gold Member

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    Accelerator Pump on the carb, seal gets bad.

    Can get a new one. Basically gives the carb a shot of gas when you first depress the gas pedal to give it some extra fuel to get it going up off the low rpms.

    When accelerator pump is wore out dried up, won't give the engine the shot of fuel it needs to get going so it stumbles to get up to rpm where it can draw fuel more easily.

    Oh yes, unscrew the low speed idle jet at the bottom outside carb. Spray some carb cleaner in there and blow out with compressed air.

    Reinstall low speed jet to the bottom and back out 1 1/2 turns as your starting point for adjusting fuel at idle.
     
    Last edited: Jul 9, 2020
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    • nitro_rat

      nitro_rat FABO Gold Member FABO Gold Member

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      Sounds like you need a new carb, a new mechanic, or both...
       
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      • Demonracer

        Demonracer 71 Demon 00 Ram 16 Chrysler 300S 05 Caravan FABO Gold Member

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        As George says, check the accelerator pump & also the bore that it rides in. With the trash ethanol gas we have, the moisture it absorbs could have pitted the bore causing it not to get the full shot of gas.
         
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        • chinze57

          chinze57 Push Button tranny and a Slant 6 that'll never die FABO Gold Member

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          I strictly use no ethanol gas because it’s easily available at my local gas station, but I doubt the previous owner knew better
           
        • Johnny Dart

          Johnny Dart Well-Known Member

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          Have you checked for any vacuum leaks ? A vacuum leak would cause your car to run poopy.
          It certainly can be fuel related to. Get a clean gas can, and run a line to the fuel pump and see how it runs.
          Take the carb off and clean it. Take out the jets, a/f , and blow compressed air through all the the passages. I'm assuming your mechanic knows how to adjust the a/f and idle correctly?
          How's your timing ?
          A well running 2bbl /6 runs well, with much more get up and go over a 1bbl.
           
        • chinze57

          chinze57 Push Button tranny and a Slant 6 that'll never die FABO Gold Member

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          My mechanic is pretty good, and he does a lot of work on classics, especially mopars.

          There is a slight vacuum leak coming from the exhaust mainfold. The exhaust manifold is slightly pitted/warped. I’m in the market to replace that with a new one and replace all the gaskets and hardware. Once that’s out of the way I can look more a time the carburetor’s performance. In the meantime I’ll check the accelerator pump
           
        • theFightingFew

          theFightingFew Always Learning/1975 Valiant Custom/1974 Valiant FABO Gold Member

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          What make/model carburetor do you currently have installed? I didn't see that mentioned anywhere...
           
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          • 66fs

            66fs FABO Gold Member FABO Gold Member

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            Can you take a picture of the carb? 73 up had adjustable primary rod holder. You can raise the rods to get more fuel. I ran a stock 2 barrel intake and carb on a souped up 170 and ran perfect.
             
          • 67Dart273

            67Dart273 FABO Gold Member FABO Gold Member

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            !!! END OF THREAD !!!

            Don't go replacing/ redesigning everything until you fix what you have and get it running right.
             
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            • slantsixdan

              slantsixdan =..=

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              These cars run and drive fine when everything's in proper repair and adjustment. Sounds like you need more repairs and adjustments before thinking of upgrades. No, slapping on a 2bbl or a 4bbl doesn't just automatically give you better or much-better acceleration, and putting on a different kind of carburetor like this is non-trivial on a '64 Dart.

              Your mechanic doesn't sound quite capable of doing what needs doing, if this is how you got the car back after he "rebuilt and tuned" the carburetor. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. Follow Tune-up parts and technique suggestions in this post. And don't forget the valve adjustment.
               
              Last edited: Jul 9, 2020
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              • barbee6043

                barbee6043 barbee 6043 FABO Gold Member

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                Sometimes you need an older mechanic also.
                 
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                • Dana67Dart

                  Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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                  What engine? (Assuming a \6)
                  What other work has been done to the car/ engine?
                  Did the car ever run as expected?
                   
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                  • George Jets

                    George Jets 1967 Dart 2 Door FABO Gold Member

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                    Readjust those valves, slant 6s have mechanical valves and they need to be adjusted. Probably been a long long time since it has been done.

                    It will just plain run better when you adjust the valves.

                    If V8 could have mechanical valves or hydraulic valves. 273s had mechanical valves.
                     
                  • nitro_rat

                    nitro_rat FABO Gold Member FABO Gold Member

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                    He's asking if switching from the one barrel to a two barrel will fix his dismal acceleration...
                     
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                    • Dana67Dart

                      Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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                      I agree but nowhere did the OP say that, it was just assumed, by me as well.

                      I'm not a \6 person but perhaps there are valuable differences between the various displacements, ( ford 170, 200, same basic eng, 300 different)

                      Still don't know what else OP has done to car / eng

                      I know I'm knit pickling but sometimes the answer is in the little things.
                       
                    • nitro_rat

                      nitro_rat FABO Gold Member FABO Gold Member

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                      OP posted a question i the /6 forum regarding upgrading his '64 Valiant to a 2 barrel carburetor. Safe to assume it's a /6. Doesn't matter if it's a 170 or a 225, a 2 barrel (or 4 barrel for that matter) isn't going to fix his issues. He needs a competent person (could be anyone, including himself) to baseline the car back to proper tune. This includes valve lash, timing, and carb settings. Until this is done, upgrades are futile. Chances are he will be satisfied with proper performance of the car in stock condition.

                      Along the same lines, I have been involved with Ford Model A's in the past. There is much to do in that sector of the hobby with "hop ups" and hydraulic brake conversions. Guys are always blown away that a "stock" A properly assembled to factory tolerances and proper tune with mechanical brakes runs and drives better than a cobbled together job with all the fancy "must have" mods. They weren't built to be a parade car! Yes, a stock Model A will both run 70 mph and lock up all 4 tires with mechanical brakes (if it's all within spec)!!!
                       
                    • RustyRatRod

                      RustyRatRod Lemmie see your b00bs. FABO Gold Member

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                      He's not good enough for me to pay. Then again, I do my own work.
                       
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                      • RustyRatRod

                        RustyRatRod Lemmie see your b00bs. FABO Gold Member

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                        I say probably not. My stone stock 170 has anything BUT dismal acceleration. It's quite snappy.
                         
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                        • Tooljunkie

                          Tooljunkie King of cobble/master of the broken bolt FABO Gold Member

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                          Stop beating on the carb and take a good look at distributor.
                           
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                          • AJ/FormS

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

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                            Or the cylinder pressure, or the elevation you are operating at. I see Wiki says the highest point in Ga is 4784 ft,while the lowest is sealevel. That's gonna make a big difference .
                            As will a 2.20 rear gear, a bad exhaust, a bad cylinder, or a bad TC. etc.
                            You need somebody competent to establish a baseline.

                            BTW
                            The SS 2bbl his tiny tiny venturies to help in making fuel mileage. With no other changes, I doubt you could measure a performance improvement over a good operating single bbl. In fact, Ima thinking my engine was stronger with the 1bbl
                             
                          • George Jets

                            George Jets 1967 Dart 2 Door FABO Gold Member

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                            Here is my "Guess"

                            3.23 rear axle ratio on a 7 1/4 rear end. 3 spd manual trans.

                            Rear cylinder compression is at 90 psi, remaining cylinders are 110 psi.

                            Rear cylinder is farthest away from the radiator so that one looses compression first over time. Will still run a long time yet.

                            Pea Shooter exhaust pipe, 1 1/2" tube.

                            Oh yeah, like @Tooljunkie said, take a look at the distributor, "Points Distributor".
                             
                            Last edited: Jul 9, 2020
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                            • chinze57

                              chinze57 Push Button tranny and a Slant 6 that'll never die FABO Gold Member

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                              I'm not sure what carb I have. I'll get photos tomorrow and post them here.
                               
                            • chinze57

                              chinze57 Push Button tranny and a Slant 6 that'll never die FABO Gold Member

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                              Damn you're good. 1 1/2" exhaust, 3spd automatic push button 727, 7 1/4 rear end and i do believe the diff is 3.23. And yes, point distribution. What's involved in changing that out?
                               
                            • chinze57

                              chinze57 Push Button tranny and a Slant 6 that'll never die FABO Gold Member

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                              I'm working on getting to doing all of my own work. This is my first car and the first car I've worked on. I saw it being abused and neglected by a kid at my high school and so I bought it off of him and I figure I'll use it to learn all I can. My mechanic has done very good work generally, but this has been my one gripe
                               
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