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    choke questions

    Here in US, I never have to pull my choke out more than or beyond fast idle about 1500 rpm) to start the car. 95% percent of the time when starting I need choke. At this fast idle stage is the choke letting in more fuel in to the engine?
    If I increase the choke beyond fast idle,, the cam increases the engine idle speed even higher. I'm assuming at this point, more fuel is getting into the engine, is it necessary to increase engine speed?

    Sujit

    #2
    Not really.

    All that is needed is enough mixture enrichment to allow the engine to pull cleanly, and enough fast idle to stop it stalling at tickover, you can adjust how much more rpms you get as you pull out the choke?

    every car will be different due to differences in the carb tune and the temperature and humidity at cold start.
    Header tanks - you can't beat a bit of bling.

    Comment


      #3
      Sujit,
      Wilf is correct. You can adjust the choke idle speed independently of enrichment. This is done by adjusting the set screw that rides the cam on the choke spindle. The more you screw it out the more revs are increased. So if you find you are pulling out the choke to stop the car stalling, but then it is revving too much, screw this set screw in. If you find you have to pull out the choke just to maintain the idle revs when cold, it may well be too rich and you should unscrew the idle speed screw. You just have to play with it.
      On my car, the cam was opening the throttle far too much as the choke was opened and I ended up filing the cam to make the profile far less aggressive. I think this is because with modern electronic ignition and running the engine 16 degrees advanced means much less extra throttle is required when cold.

      Comment


        #4
        I’m not sure how far you need to pull it to start enrichment but you could remove the choke mechanism easily by just undoing 2 screws. Look inside and you will see 4 tiny holes, these are what enrichen the mixture. Then you can work out just how far to pull it to get to the first hole. Once you know that then set the idle adjuster at that point, say 1500rpm that way you know that if you pull the choke to make it run 1500 then you have at least opened up the first enrichment point..

        So far my coldest start was on Sunday at around 55 degrees (probably mid winter in California!!) and like you I just pull it enough to give a bit of extra idle, not far at all..
        Terry Hunt, Wilmington Delaware

        www.terryhunt.co.uk

        Comment


          #5
          Adjust the cam bolt to suit your local cold start conditions.
          Mine starts cold with a small amount of choke at about 900rpm.
          fwiw it’s more important for an auto that you might want to move when still on choke.
          There are 2 secrets to staying on top :- 1. Don't give everything away.
          2.

          Comment


            #6
            I currently have 2 issues with Stag no.1. Its an auto. Engaging a gear at 1500 rpm is not very nice and now the choke cable during fast idle doesn't stay put. The cable doesn't lock in place. It never locked but the friction held it in place.

            I was going by the ROM to set up the carbs on Stag no. 2. but it looks like people adjust to suit their needs. However, I'll use the ROM as a datum.
            MikeP , I thought about changing the profile of the cam, but kept quiet.
            Sujit

            Comment


              #7
              Sujit,

              I think 1500 rpm is far too high for cold idle and will waste fuel. And mine is a manual so I don't have to worry about the car driving off! The reason I adjusted the cam profile was to keep idle at around 1000rpm under all choke conditions. My normal idle is around 800rpm.

              Comment


                #8
                Sujit,

                1. Why doesn't your choke lock? It should lock by turning it approx 1/4 turn clockwise. It should be free moving when unlocked.

                2. 1500 rpm is way too high - especially if you have an auto. My car usually needs full choke to start (always instant) and then immediately push in to about half way then ease in to 1/4 when under way, after about a mile all the way in. Max fast idle with the choke is around 850 rpm - nice and smooth even when really cold. Normal idle when hot is around 500 rpm. As others have said adjust the small bolt under the cam, screw it in to reduce the revs. Idle revs drop by about 50 rpm when you engage drive or reverse. Mine has the BW35 box.

                Roger
                White TV8 BW35 no mods and now a Dolly Sprint to keep it company
                So many cars, so little time!

                Comment


                  #9


                  My choke does not lock, could be wrong but I thought it may be original as it has the solid wire. The other one I have that is braided does not lock either.. both rely on friction.

                  Terry
                  Terry Hunt, Wilmington Delaware

                  www.terryhunt.co.uk

                  Comment


                    #10
                    Hi Mike, I have a spare cam on my desk and have been pondering on changing the profile to maintain a constant engine speed for all choke conditions just like you have, and it seems it is possible. I was just wondering why the current factory cam profile increases the engine speed as you use more choke.

                    Roger, Stag no. 1 BW auto choke has never locked. I don't want to take it apart as the wires are frayed at the ends and I'll never get them back through. Stag no.2 has an after marker choke and does look.

                    I'll look into reducing the RPM over the next few weekends.
                    Regards, Sujit


                    ​​​​​​​

                    Comment


                      #11
                      Sujit,
                      You do need to open the throttle more when the engine is cold to maintain the same revs. Probably because of a number of factors. The oil is thicker for a start and so friction is higher. My problem with the standard profile is that it increases revs too much particularly at the more fully choked position. So basically it needs a certainl increase in throttle opening right from the smallest choke opening and then a very gradual rise thereafter. I am surprised more haven't encountered this issue. Be interesting to see what you find best.

                      Mike

                      Comment


                        #12
                        Hello MikeP.
                        I'm assuming the easiest way to change the profile is to remove the cam, get a compass, center it on the hole, where the shaft goes through, and scribe a line and then get the angle grinder out. Is this how you did it?
                        Regards, Sujit

                        Comment

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