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  • 4100 autolite help

    Hi again gents, wasn't sure if I should start a new thread or stay on my older one "carburetor question" from 11-4-12. BTW, happy new year!

    I took your advice and rebuilt the 4100 I bought used. A note that was with it said it was from a 67 T-bird 390. Other than a bent secondary vacuum pickup tube it seems perfect. The rebuild went very smoothly and I feel good knowing that all the little passage ways are clean and flowing great. I put it on yesterday (in the snow) and it fired right up. I could instantly feel a better throttle response, and I hadn't even adjusted it.

    Here's my problem though. I can't get it to idle lower than about 8000 rpm. I drove it around and it got good and hot, and the choke was fully opened. I can back off the throttle screw until it isn't seated anymore, then back off the secondary throttle screw too, but unless I push on the secondary throttle screw head it stays idling at about 8000. This carb is a little different from the original in that it has a hex head screw that screws into a plastic piece that seems to tie in with the fast idle cam and bellcrank lever. Here's a few pictures of my setup, and my throttle linkage.

    At any rate, can anyone point me at what to look for first when the idle is so high?

    Oh wait, I just re-read page 2-30 and noticed that I never set the secondary throttle plate per instructions - that sure looks like it could be my problem. Yes? no?

    I'll post this anyways, and go check it now.

    thx, Dave J
    Attached Files

  • #2
    My first thought was that the secondaries were open too much. You're right about the adjustment. It is often missed and best done with the carb upside down.
    Carl

    Comment


    • #3
      Yeah, I can get to it with a little bent screwdriver but I can's quite turn it.

      Any idea on how to adjust the little hex head screw that goes into the plastic piece and seems to be for the choke?

      thx, Dave

      Comment


      • #4
        Slightly fast 'idle'???

        I can't get my 390 to rev to 8000rpm - let alone 'idle' at that speed!!!
        A Thunderbirder from the Land of the Long White Cloud.

        Comment


        • #5
          Well maybe you should rebuild your carb Tom. Could have something to do with you being on the good side of the equator right now.
          ;0)

          Anyway, after warming up it idles just below 750 rpm now. I think that's good considering it's 27 degrees outside.

          I figured out that the little hex head screw allows me to adjust the choke to be fully open after warming up - I think that's all it's for.

          The BIG question I have now is how can I tell if the secondary's are working?

          I pulled over, removed the air cleaner, and floored it - but I don't see them opening at all. When I was rebuilding the carb I sucked on the the vacuum hole and it pulled the diaphragm as it should. This carb does not have the check ball on the secondary as the manual describes for the 1959 carb so it's not that.

          thx for any help, Dave J

          Comment


          • #6
            Originally posted by davidmij View Post
            Well maybe you should rebuild your carb Tom. Could have something to do with you being on the good side of the equator right now.
            ;0)

            Anyway, after warming up it idles just below 750 rpm now. I think that's good considering it's 27 degrees outside.

            I figured out that the little hex head screw allows me to adjust the choke to be fully open after warming up - I think that's all it's for.

            The BIG question I have now is how can I tell if the secondary's are working?

            I pulled over, removed the air cleaner, and floored it - but I don't see them opening at all. When I was rebuilding the carb I sucked on the the vacuum hole and it pulled the diaphragm as it should. This carb does not have the check ball on the secondary as the manual describes for the 1959 carb so it's not that.

            thx for any help, Dave J
            'Flooring' it is unlikley to cause the secondaries to open, it need a load on the motor to cause that.

            The secondaries don't come into play much in daily driving i.e. around town etc.

            It's when you floor it to pass another vehicle etc that the carck open.
            A Thunderbirder from the Land of the Long White Cloud.

            Comment


            • #7
              I found a couple of idea's on testing a vacuum secondary. Put a dab of white grease on the actuator arm at the cover and see if it gets smudged. Or, put a paper clip on the actuator rod up against something and see how much it moves - that will tell you how far it's opening. One more, and this one might be best with the autolite, is to loosely put a piece of masking tape across the hinge part of the actuator arm and actuator rod to see if it pulls apart.

              I also read that it should be a fairly smooth transition when they kick in, thus it's hard to tell by feel. And having a loud exhaust makes it almost impossible to hear the suction sound.

              I'll try these this weekend and see. That is if the weather gets above freezing. I can drive the car for for 15 minutes and the intake barely even gets warm due to my closing off of the exhaust bypass. Tough to get it up to operating temp.

              One thing is for sure, rebuilding the carb has given me a lot better throttle response, and plenty of power to spin the wheels. I'd like to find some where nearby where I could check the 1/4 mile time now that it's running smoothly. I know it's far from fast by today's standards, especially weighing 3800 pounds - but I'd still like to know. I'd also like to see how it dyno's.

              The base motor was 315hp and 427 ft lbs. I replaced the heads with C4AE 6090G‎. Added FPA headers. I also put in a 1 3/8 shaft - close ratio - 4 speed toploader and changed out the 3.10 rearend for a 3.89.

              Dave J

              Comment


              • #8
                Originally posted by davidmij View Post

                I found a couple of idea's on testing a vacuum secondary. Put a dab of white grease on the actuator arm at the cover and see if it gets smudged. Or, put a paper clip on the actuator rod up against something and see how much it moves - that will tell you how far it's opening. One more, and this one might be best with the autolite, is to loosely put a piece of masking tape across the hinge part of the actuator arm and actuator rod to see if it pulls apart.

                I also read that it should be a fairly smooth transition when they kick in, thus it's hard to tell by feel. And having a loud exhaust makes it almost impossible to hear the suction sound.

                I'll try these this weekend and see. That is if the weather gets above freezing. I can drive the car for for 15 minutes and the intake barely even gets warm due to my closing off of the exhaust bypass. Tough to get it up to operating temp.

                One thing is for sure, rebuilding the carb has given me a lot better throttle response, and plenty of power to spin the wheels. I'd like to find some where nearby where I could check the 1/4 mile time now that it's running smoothly. I know it's far from fast by today's standards, especially weighing 3800 pounds - but I'd still like to know. I'd also like to see how it dyno's.

                The base motor was 315hp and 427 ft lbs. I replaced the heads with C4AE 6090G‎. Added FPA headers. I also put in a 1 3/8 shaft - close ratio - 4 speed toploader and changed out the 3.10 rearend for a 3.89.

                Dave J
                Dave,

                As for that adjusting nut, you need to refer either to the Shop Manual for that year carb or the instruction sheet (FORD) for the MOTORCRAFT carb kit. I thought I scanned and posted it here at one time?

                Kinda makes for rough driving in cold weather without the heated crossover doesn't it? You will have to run the choke a little tighter during cold weather and lean it out in the spring.

                As for the secondaries, it should be an un-noticeable transition if set properly. If they open too soon, there will be a bog and if late, a lack of performance and the transition being noticeable (delayed).

                Uh... A few photos would be nice...

                Comment


                • #9
                  ...forgot...

                  You said there is no check ball in the secondary circuit?

                  Camshaft choice?

                  Comment


                  • #10
                    Thx Gary,
                    there are a few pictures of the choke area, and the hex head screw and plastic piece in the #1 post. The top two pictures are with the carb off before I rebuilt it - they also show the manual choke. The second two pictures are with the carb on the car and with the thermal choke.

                    This carb is supposedly from a 67 T-bird, and my old one was from a 67 LTD - they are both identical other than this one had a manual choke. I think I'm going to put the manual choke back on it because I have headers on the car and my rigged up heat tube is just open at the hot end. Don't want it to be sucking up dust and dirt.

                    Yes, this carb does not have the secondary check ball. My manual is for a 59 t-bird which says the 59 did have one.

                    From what you and others wrote I'm pretty sure the secondaries are working fine. The car has a very good feel power and running wise when I step on the gas. Doing the rebuild and using the manual really helped me get a feel for how everything works and ties together. I just wanted to be sure that the secondaries were working, I'll try the tricks I found as soon as the weather warms a bit. It doesn't stay this cold here for very long. And your are right, it does make for rough driving when it's really cold! When the car is warm and idling it gives the occasional pop sound, almost like it has a non stock cam. I think that's just because the choke is still a little shut. It doesn't stutter or miss at all when I hit the gas.

                    It's nice to be able to pump the pedal a couple of times and fire it right up without having to ride the pedal when it's cold. Then seeing the choke working correctly, and the fast idle cam go through it's progressions as it should.

                    If you want some specific photos just let me know and I'll post them. I took tons of pictures as Simplyconnected always advises.

                    thx a ton, Dave J

                    Comment


                    • #11
                      rigged up heat tube is just open at the hot end


                      I think with your setup, the manual choke will be better. Does it have an orgional appearing choke cable/handle to look period correct?

                      I meant to show you detail on how to make a nice looking choke stove but you got the headers in before I could reply.

                      HOLLEY used to make a cap to go over the vacuum inlet that included a small filter. It just used under hood heated air and not choke stove. That might be another option.

                      Glad it all worked out for you...

                      Comment


                      • #12
                        I'm not really sure if it's an original appearing manual choke - you can see it in the second picture.

                        Comment


                        • #13
                          I've rebuilt a ton of 4100 carburetors from '58 on up and I've never seen one with a secondary check ball. The picture in my '59 shop manual doesn't show one. Where did you see it.

                          John
                          John Pizzi - Squarebirds Administrator

                          Thunderbird Registry #36223
                          jopizz@verizon.net 856-779-9695

                          http://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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                          • #14
                            There is a check ball to prevent diaphragm damage in case of a backfire.

                            Comment


                            • #15
                              Originally posted by davidmij View Post

                              I'm not really sure if it's an original appearing manual choke - you can see it in the second picture.
                              I meant the cable housing and knob asm on the interior to make it appear as a factory install.

                              The choke kit you have is a make-do. It uses the original choke cap. I would show you a photo of an original HI-PO piece, but...

                              You know, why I am thinking about it, the carb may be too lean (jetting). Usually headers makes one breath a lot deeper and it requires a richer mixture.
                              Last edited by KULTULZ; January 5th, 2013, 01:59 PM.

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