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Avanti bogs down under full throttle - update

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  • #31
    We'll definitely try moving the timing up 4-5 degrees and see what happens. What setting do you recommend for the vacuum advance? As you can see in the previous note, an undersize carb pump might be part of the problem too. Thanks!


    quote:Originally posted by bige

    If you had an accelerator pump problem symptoms would show up in off idle acceleration and light throttle acceleration at cruising speeds. If you aren't experiencing these symptoms I wouldn't concentrate on the accel pump.

    The Mallory can be made to work just fine by using the adjusting kit. Mine has a total of 14 degrees centrifugal and I run 14 degrees static. I'm all in at 28 degrees about 1900 RPM. Some track testing verified those settings work for MY car.

    You can't get too hung up on factory recommended numbers. If your car runs best at 8 degrees at idle and 28 at 1600 then set it that way, assuming you don't have a detonation problem or a labored crank. I've had both the Mallory and a Delco window and in both cases in order for my car to run as it should I had to run much more static timing while limiting the total timing.

    From a performance standpoint more compression is a good thing. Your combination may present some tuning issues in warm weather driving under boost but in general acceleration and throttle response improve with higher compression not deteriorate.

    Just move the distributor and advance the timing 4-5 degrees and see if there's an improvement so you can either concentrate on the distributor or move to fuel. Your transmission/torque converter is not causing your bog.

    Also, I would expect to see a different amount of fuel Quadrajet vs. AFB. The Q jet has tiny primaries causing lots of velocity and opening one on a stationary car would not allow the secondary air valve to open unless you were crazy enough to hold it at full throttle for a few seconds, at least. So there's a ton of air streaming past those primary venturis pulling lots of fuel with it.

    Find a distributor position where your car runs best. Make note of the number at idle setting, the 1600 to 2000 range numbers and check the total advance at 3000 rpm. Just because it's ok at 1600-2000 doesn't mean it will stay there. If your car like 8 degrees static. or whatever number, then adjust the distributors total advance so that you get no more than the 24 at 1600-2000 and beyond. Vacuum advance does not have any effect on wide open throttle acceleration.

    If no amount of timing adjustment cures the bog you must look at fuel delivery.

    ErnieR

    edp/NC
    '63 Avanti
    '66 Commander
    edp/NC
    \'63 Avanti
    \'66 Commander

    Comment


    • #32
      The timing was checked with the vacuum advance hose removed. Many people have used the T-bow Mallory with great success. So I'm not gonna remove a $400 investment. Thanks.

      quote:Originally posted by KOOL R2

      EDPJR

      Please refer to my previous post. I think that timing and your distributor are the cause.

      The timing is set at 24 degrees at 1600 rpm with the VACUUM HOSES DISCONNECTED.
      If you set the timing with the hose connected your timing would be retarded when you accelerated. This would cause the bog.
      To compound the problem the Factory settings on the Mallory have a centrifugal advance of 24 degrees. This is way too much for am R2
      I would remove the Mallory and install a dual point Prestolite or a Delco Window unit with a Pertronix conversion

      Peter Sant
      KOOL R2
      edp/NC
      '63 Avanti
      '66 Commander
      edp/NC
      \'63 Avanti
      \'66 Commander

      Comment


      • #33
        An accel pump could exacerbate the issue but if your car accelerates without hesitation from a dead stop I would think you're OK. The pump is there to help the engine transition from fuel fed by the idle ports to fuel drawn through the venturis as you open the throttle blades and the down-rushing air sucks the fuel through the venturi clusters and has less impact as speed increases because you have air passing over the venturis drawing fuel already.

        The pump shot is best checked with the car off. It should be a stream not a dribble, if you can you can hear it and see it that's the best. It should occur with the slightest movement of the linkage for best response and last through a good portion of linkage travel from closed to wide open. The 's' clip that attaches the pump arm to the pump itself can be bent a little to remove some slack. How far up the pump goes in the bore is important also. It needs to have enough travel to allow a nice volume of fuel under the 'umbrella'.

        Just a thought on factory timing settings. As a child of the 60's reading voraciously every magazine road test I could get my hands on ( I still have the magazines ) one thing that I always noticed on road tests that were looking for maximum performance was the first thing the testers did was either advance the timing or re-curve the distributor entirely. The manufacturer generally set the car up for good overall performance, economy, ability to run on poor grade fuels, the widest coverage with off the shelf distributors etc. In other words a good compromise for various altitudes, temperatures driving habits and reduced warranty claims.

        So even on a car that has no particular issues playing with the timing a little and straying from factory specs can make for a better performing car. If not...you put it back where it was.



        1988 "Beater" Avanti---R5388 @ Macungie 2006

        Comment


        • #34
          With respect to the accelerator pump, the leather ones are very difficult to get to work properly and modern gas only seems to exacerbate this.

          If you look at all the new Edelbrocks and Carters you'll see that they use some sort of rubber umbrella/plunger. I went through kit after kit trying to find a leather version that fit well a number of years back. Even tried all the umbrella break-in tricks in the book and still had no luck.

          I wonder if one could adapt a new Edelbrock/Carter plunger to the old carb?

          http://community.webshots.com/user/s...host=community

          Comment


          • #35
            My brother doesn't like the way the leather pump fits or works either. The kit I got didn't provide a replacement ball valve. Does anyone know where I can get a different type pump or another R2 carb kit? Thanks! [^]


            quote:Originally posted by wcarroll@outrageous.net

            With respect to the accelerator pump, the leather ones are very difficult to get to work properly and modern gas only seems to exacerbate this.

            If you look at all the new Edelbrocks and Carters you'll see that they use some sort of rubber umbrella/plunger. I went through kit after kit trying to find a leather version that fit well a number of years back. Even tried all the umbrella break-in tricks in the book and still had no luck.

            I wonder if one could adapt a new Edelbrock/Carter plunger to the old carb?

            http://community.webshots.com/user/s...host=community
            edp/NC
            '63 Avanti
            '66 Commander
            edp/NC
            \'63 Avanti
            \'66 Commander

            Comment


            • #36
              quote:Originally posted by edpjr

              My brother doesn't like the way the leather pump fits or works either. The kit I got didn't provide a replacement ball valve. Does anyone know where I can get a different type pump or another R2 carb kit? Thanks! [^]


              quote:Originally posted by wcarroll@outrageous.net

              With respect to the accelerator pump, the leather ones are very difficult to get to work properly and modern gas only seems to exacerbate this.

              If you look at all the new Edelbrocks and Carters you'll see that they use some sort of rubber umbrella/plunger. I went through kit after kit trying to find a leather version that fit well a number of years back. Even tried all the umbrella break-in tricks in the book and still had no luck.

              I wonder if one could adapt a new Edelbrock/Carter plunger to the old carb?

              http://community.webshots.com/user/s...host=community
              edp/NC
              '63 Avanti
              '66 Commander
              Dave TBow has good kits.
              http://www.stude.com/Tbow/

              JDP/Maryland
              JDP Maryland

              Comment


              • #37
                Thanks. I ordered a carb kit from Dave Thibeault today. He says it will be complete and better than the other one we used. I sure hope so. My brother says the car is running lean. We'll adjust the timing too. And, if none of these changes fix the problem, I can try the R2 Carter fuel pump I've got that must have originally come from Jon Myer (it has his name on the box). [|)]

                quote:Originally posted by JDP

                quote:Originally posted by edpjr

                My brother doesn't like the way the leather pump fits or works either. The kit I got didn't provide a replacement ball valve. Does anyone know where I can get a different type pump or another R2 carb kit? Thanks! [^]


                quote:Originally posted by wcarroll@outrageous.net

                With respect to the accelerator pump, the leather ones are very difficult to get to work properly and modern gas only seems to exacerbate this.

                If you look at all the new Edelbrocks and Carters you'll see that they use some sort of rubber umbrella/plunger. I went through kit after kit trying to find a leather version that fit well a number of years back. Even tried all the umbrella break-in tricks in the book and still had no luck.

                I wonder if one could adapt a new Edelbrock/Carter plunger to the old carb?

                http://community.webshots.com/user/s...host=community
                edp/NC
                '63 Avanti
                '66 Commander
                Dave TBow has good kits.
                http://www.stude.com/Tbow/

                JDP/Maryland
                edp/NC
                '63 Avanti
                '66 Commander
                edp/NC
                \'63 Avanti
                \'66 Commander

                Comment


                • #38
                  Indeed, this T-bow kits looks far better and complete. I suspect the top will be coming off the old 4V-AFB again pretty soon for re-work. I've also got a new Carter fuel pump for an R2. If these two items don't get gas flowing properly, I don't know what will. We'll also turn up the timing a few degrees. Wish me luck. [^]

                  edp/NC
                  '63 Avanti
                  '66 Commander
                  edp/NC
                  \'63 Avanti
                  \'66 Commander

                  Comment


                  • #39
                    quote:Originally posted by edpjr

                    Indeed, this T-bow kits looks far better and complete. I suspect the top will be coming off the old 4V-AFB again pretty soon for re-work. I've also got a new Carter fuel pump for an R2. If these two items don't get gas flowing properly, I don't know what will. We'll also turn up the timing a few degrees. Wish me luck. [^]

                    edp/NC
                    '63 Avanti
                    '66 Commander
                    Electric pump in the rear, most every R2 I've had needed one, the Salt Flats cars had three.

                    JDP/Maryland
                    JDP Maryland

                    Comment


                    • #40
                      Then do you block off the mechanical pump? If so, what do you do with the line that goes to the super-charger? Who sells the proper electric pump? [?] Thanks.


                      quote:Originally posted by JDP

                      quote:Originally posted by edpjr

                      Indeed, this T-bow kits looks far better and complete. I suspect the top will be coming off the old 4V-AFB again pretty soon for re-work. I've also got a new Carter fuel pump for an R2. If these two items don't get gas flowing properly, I don't know what will. We'll also turn up the timing a few degrees. Wish me luck. [^]

                      edp/NC
                      '63 Avanti
                      '66 Commander
                      Electric pump in the rear, most every R2 I've had needed one, the Salt Flats cars had three.

                      JDP/Maryland
                      edp/NC
                      '63 Avanti
                      '66 Commander
                      edp/NC
                      \'63 Avanti
                      \'66 Commander

                      Comment


                      • #41
                        My Holley Blue fuel pump came with a regulator. I took the adjusting screw on the top of the regulator, drilled a hole in it and soldered a short piece of steel tube in it. This allows you to run a hose from the pressure side of the supercharger into the regulator. The regulator will then "read" the higher pressure as atmospheric pressure and deliver fuel at 6 lbs above whatever pressure is being delivered to the regulator.

                        sals54
                        sals54

                        Comment


                        • #42
                          Unfortunately, if you do all 3 operations, timing, fuel pump and accel pump, all at once you'll never know what the original problem was. It would be a valuable lesson for all involved to know the true solution.

                          ErnieR

                          Comment


                          • #43
                            if it is an accel pump *bore* problem you may have to have the accel pump hole reamed and sleeved. Not sure who is able to do this, I have never bothered.

                            As Sal said, if you go with only an electric pump, you should have a boost-referenced regulator near the carb. Fortunately you already have a return line installed to make this somewhat easy.

                            nate

                            --
                            55 Commander Starlight
                            http://members.cox.net/njnagel
                            --
                            55 Commander Starlight
                            http://members.cox.net/njnagel

                            Comment


                            • #44
                              quote:Originally posted by edpjr

                              Then do you block off the mechanical pump? If so, what do you do with the line that goes to the super-charger? Who sells the proper electric pump? [?] Thanks.


                              quote:Originally posted by JDP

                              quote:Originally posted by edpjr

                              Indeed, this T-bow kits looks far better and complete. I suspect the top will be coming off the old 4V-AFB again pretty soon for re-work. I've also got a new Carter fuel pump for an R2. If these two items don't get gas flowing properly, I don't know what will. We'll also turn up the timing a few degrees. Wish me luck. [^]

                              edp/NC
                              '63 Avanti
                              '66 Commander
                              Electric pump in the rear, most every R2 I've had needed one, the Salt Flats cars had three.

                              JDP/Maryland
                              edp/NC
                              '63 Avanti
                              '66 Commander

                              I keep the stock pump, just add a low pressure or regulated pump near the tank to assure fuel flow. It helps for quicker starts and vapor lock too. Check some of the other suggestions to0.

                              JDP/Maryland
                              JDP Maryland

                              Comment


                              • #45
                                Correct me if I'm wrong. Your problem occurs when you are cruising along at 40 mph or so and you put your foot to the floor and at that moment the car bogs but then takes off as it's supposed too? If that's the case you do not have fuel pressure issue. Look at the logic of it. While cruising fuel demand is low the bowls are full. When you put your foot down the car has not reached a level where demand is outpacing fuel delivery. Also if I read correctly it doesn't bog when you downshift manually so how come fuel pressure is OK then? Your car and money but poor fuel pressure does not cause the problem you are experiencing if I understood it correctly



                                1988 "Beater" Avanti---R5388 @ Macungie 2006

                                Comment

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