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    carb and choke

    1967 Fastback with 390 and 650cfm Holly Steet Avenger carb.

    ive got two issues which, may or may not be related:

    cold start - a compete bitch and takes about 12 miles of driving before warm enough to not cut out. I'm not sure that the electric choke is working at all... I'm no thanks very knowledgeable about it... where should I start ? What are the basic principles of the electric choke ?

    warm running - great... but as you pull up so from 50mph to 0 and a roundabout of junction the engine cuts out as through staved of pertol. If you rev up a fair bit as you down shift to first you just about avoid the cut out...

    thoughst anybody ?

    thanks,

    Simon

    #2
    Hi Simon,

    Sounds very much like fuel starvation to me - perhaps a bit of grit in the carb or something.
    Cold start needs a richer mixture - I have my 289 choke wired open (so not used) but even so it only takes a couple of minutes for the engine to warm up enough not to need a bit of throttle to stop it stalling - 12 miles is a long old distance. Is the engine showing warm much before then?
    Coming to a junction is similar - assuming you have a mechanical fuel pump then it will suddenly pump far less fuel and more likely to stall.
    You could try removing the air filter and spraying some carb cleaner down the carb to rid it of any tarnish build up, but if it's grit at the needle that might need more disassembly work to clear.
    One other thought is how old your carb is - it's possible that one or both the floats have deteriorated and the fuel levels are low.
    As adjustment involves running the engine and a slight dribble of fuel from the carb side plugs it's best done with some care, but not a difficult job if you take things slowly.

    If the car was running and pulling fine before I'd start with that - or other suggestions posted.
    If it's not felt to be "on song" for a while then maybe have a full tune-up done - there are posts about how to do that and it can be satisfying to go through it. Great to drive afterwards too, when it really pulls on the vacuum secondaries :)
    Basically you start with engine off adjustments - butterfly valve opening fully to 90 degrees with throttle pedal to the floor, 15 thou gap on accelerator pump, then set the float levels, the mixture screws VERY carefully fully in (just bottomed - they're fragile screws) then out 2 1/4 turns back out to start, then set the idle speed.
    I've probably forgotten something but that's the basics, but of course you can't beat a proper set up on a rolling road.

    Hope it proves to be an easy fix.
    Simon
    '65 289 "A" Code GT Optioned Coupe, with 4spd Toploader and Arvinode exhaust - sounds great! :D :gears

    Comment


      #3
      Hi SurreyXedos,
      yep thanks for that.. I'll go through that process and see how it goes but also get a rolling road tune up booked in. I don't think the choke is working at all... in term sof age and conditin I'm not sure when the carb was last serviced but it's a period, early original Street Avenger... could be 50 years old for all I know...

      cheers


      Simon

      Comment


        #4
        Personally wouldn't bother with a rolling road. It's easy enough to do it without, have you got a timing light, vac gauge and 13/16th plug socket?

        all they'll do on a road is hit it with a timing light and tell you you're running rich or lean which you can tell off vac gauge and plug colour
        https://www.instagram.com/chevelle_hell/

        Comment


          #5
          Simon, You asked about the principle of the electric choke. It is very simple. The heart of the choke is in the black cylinder on the side of the carb, it is a bi-metalic coiled strip element which when heated by electric current from the car uncoils and opens the choke. It takes a little while to uncoil so giving the engine time to warm up. Many people think that by disconnecting the wire that the choke is disabled and off. It is not, pulling off the wire will mean the choke staying full on. The first thing I would do is check you have 12v on this wire when the ignition is turned on. With the engine cold if you leave the ignition on for a couple of minutes then you should see the choke begin to open. Sometimes to help the choke full close when cold gently depress the throttle a little and the choke should fully close. Others have covered adjusting the carb if that is the problem
          Allan

          Comment


            #6
            Originally posted by nomiskx View Post
            1967 Fastback with 390 and 650cfm Holly Steet Avenger carb.

            ive got two issues which, may or may not be related:

            cold start - a compete bitch and takes about 12 miles of driving before warm enough to not cut out. I'm not sure that the electric choke is working at all... I'm no thanks very knowledgeable about it... where should I start ? What are the basic principles of the electric choke ?

            warm running - great... but as you pull up so from 50mph to 0 and a roundabout of junction the engine cuts out as through staved of pertol. If you rev up a fair bit as you down shift to first you just about avoid the cut out...

            thoughst anybody ?

            thanks,

            Simon
            It could be that the carb mixture is set/running too weak, referencing in particular when you say the car cuts out after coming to a junction, roundabout etc from travelling at speed. This also could be why the car takes so long to become responsive from cold. Check to see if spark plugs are grey /have no colour on them which would show mixture is too weak. Many V8's run with choke disconnected, whether beneffficial or not, but generally start with several pumps of accelerator pedal, and need a short while to become throttle responsive. The cutting out after slowing from higher rpm is a definite sign of weak mixture. Another area to look at for these symptoms could also be a vacuum leak. Paul.

            Comment


              #7
              Ah yes, the vacuum secondaries seem to not come in as they used to either. Itís a really old carb so might go gif a full overhaul or replace .

              i think the 390 needs a 600cfm or 750cfm ?

              Comment


                #8
                Whilst they are called vacuum secondary's on these carbs they don't work off manifold vacuum. They work off the vacuum generated at the throat of the primary choke venturies. So the flow of air has to be very high in the primary chokes for the secondary's to open, you won't see them opening if you just blip the throttle either. You will have to be on a rolling road and pulling hard on the dyno to see them opening. To test if they are opening you can put a paper clip on the actuating rod where the rod goes through the top of the carb. Go for a run and give it full throttle then look at the paper clip. If its moved down the rod the secondary's are opening ok.
                Allan

                Comment


                  #9
                  If you are looking for a carb. keep your eyes open for an Autolite 4100. I have one on my '67 289 and also acquired a 600cfm version (from a 65 T-Bird) to drop on a 390 that I'm building. Good mileage and performance. Basically fit and forget. Last touched it about 3 years ago. Had a bunch of Holleys on various cars and always seemed to be messing with them.

                  Eddie

                  Comment


                    #10
                    I have a Quickfuel 650 or 750cfm 4160 carb sat on my shelf currently if its any interest to you, will check part number if wanted
                    https://www.instagram.com/chevelle_hell/

                    Comment


                      #11
                      Originally posted by EddieCross View Post
                      If you are looking for a carb. keep your eyes open for an Autolite 4100. I have one on my '67 289 and also acquired a 600cfm version (from a 65 T-Bird) to drop on a 390 that I'm building. Good mileage and performance. Basically fit and forget. Last touched it about 3 years ago. Had a bunch of Holleys on various cars and always seemed to be messing with them.

                      Eddie
                      My Cobra's 289 still runs the original '63 Autolite 4100, and it's the nicest 4-barrel I've ever had. I particularly like being able to take the entire top off to set float levels whilst the engine's idling. Got completely fed up with soaking everything in petrol every time I wanted to try a jet change in a Holley. As long as the car is relatively stock, the 4100 is the carb designed for it, so no concerns over sizing etc.

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