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    Fuel Mixture Balance

    Morning folks,

    Is there simple way to check/correct the fuel mixture balance on my Stromberg carbs? It's a May 1977 model.

    Brian
    My car never breaks down, it just occasionally fails to proceed.

    #2
    Donkey. You will need to see that they are equally "Open" at tick over before you can check the mixture. Do this by disconnecting the adjustable link rod end. Then set back the two adjusting screws till each carb is closed. Now turn up the screws in turn till you can see the linkage arm on each carburettor just starting to move. Now advance each screw 1.5 turns. If necessary, set the length of the adjustable link rod so that it can be re fitted without moving either carburettor. Then run up the engine till it is at working temperature, and turn each adjusting screw by the same amount to get a tick over of around 750 RPM. Then;
    Without access to a CO meter, this is what I do.. Unscrew the damper on each dashpot in turn. Lift it a bit, then cant it to one side and hold it there so that the piston locks in the oil filled tube. Now, when you lift any further, the piston should rise as well. (Don't overdo it and bend the rod!). Lift the piston very slightly. If the mixture is too rich, the engine speed will increase. If it is too weak, it will probably stall. Only a slight change will show that all is well.
    You will need the right tool for the job if they need re-setting. Then top up the dashpots with 20/50 engine oil. The piston should start damping when the threaded cap is no more than 1 cm. from the top of the carb.
    Mike.

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      #3
      Fully agree with the above method, but l find that 20/50 is a little on the thick side.
      my preference is 3 in 1 oil or AT
      Phil

      Comment


        #4
        Thanks Lingen - I keep meaning to check my mixture but keep putting it off because of all the disassembling of air filters, elbows etc to be able to lift the pistons. That is a much easier solution. I wish the carbs had lifting pins like on my old Spitfire of years ago! I use damper pot oil from Burlens so that should be the correct viscosity - it's probably just 3 in 1 with a huge mark up!.
        Jon

        Comment


          #5
          Folks.
          I said 20/50 because that is what Triumph say in the instructions. Thinner oil has always been specified on S.U.s, but I like to believe that Zenith had carefully done their research in order to get the best air/fuel mixture under acceleration with their equipment. Thinner oils will only weaken it in these circumstances. Is that a good thing?
          Mike.

          Comment


            #6
            Hi Brian,

            everyone has his own experience on setting up the carbs I think (!) but I can only recount that my Stag only really blossomed when I borrowed a CO meter and set up the carbs that way. I was astounded at how big the difference was after just a miniscule turn of the needle screw. Using the CO meter really transformed the running and there was no way I could have achieved that with the good old "lift the piston and see what happens to the revs" method. As doing the actual adjustment is easy, maybe your local "Contrôle Technique" might let you have a fiddle for a modest contribution to the coffee kitty!

            Regarding the oil, I used SAE20 like the original Zenith damper oil.

            Drew

            If you can't say something nice, don't say it !

            Comment


              #7
              Thanks everyone, helpful as ever.

              Kind regards,

              Brian

              PS
              Nice tip Drew.
              My car never breaks down, it just occasionally fails to proceed.

              Comment


                #8
                [QUOTE=dasadrew;n752659]Hi Brian,

                everyone has his own experience on setting up the carbs I think (!) but I can only recount that my Stag only really blossomed when I borrowed a CO meter and set up the carbs that way. I was astounded at how big the difference was after just a miniscule turn of the needle screw. Using the CO meter really transformed the running and there was no way I could have achieved that with the good old "lift the piston and see what happens to the revs" method. As doing the actual adjustment is easy, maybe your local "Contrôle Technique" might let you have a fiddle for a modest contribution to the coffee kitty!
                Regarding the oil, I used SAE20 like the original Zenith damper oil.
                Drew

                I agree with Lingen, I have always used the same oil that I put in the engine for topping up the carbs.
                Drew - I would be interested if you could enlarge on how you got the correct balance using a borrowed CO meter - ie. Did you put the CO meter in the exhaust, then make adjustments on the carbs, or did the CO moter work another way, and what reading(s) said that you had got it right?.
                ****************************************sigpic*************************************

                Comment


                  #9
                  Originally posted by Phil S View Post
                  Fully agree with the above method, but l find that 20/50 is a little on the thick side.
                  my preference is 3 in 1 oil or AT
                  Phil
                  + 1
                  sigpic

                  Comment


                    #10
                    Terry, I used Klaus' Bosch CO tester https://www.ebay.de/itm/ABGASTESTER-...cAAOSwZs5ZifdH which measures the CO at the exhaust pipe. I set it to 3.0% and it runs like a dream.

                    Drew
                    If you can't say something nice, don't say it !

                    Comment


                      #11
                      Thanks for info & Link - bit expensive to buy, will have to see if I can borrow one, purely out of curiousity,
                      as my car runs well but don't know whether it could run even better.
                      ****************************************sigpic*************************************

                      Comment


                        #12
                        I wondered whether the mixture on my car was correct but presumably when I take for the MOT they'll give me a print out which will give me an idea.

                        Richard

                        Comment


                          #13
                          I used a wide band lambda meter on my mini turbo project, it was a must for that, especially as I was adjusting the needle profiles. So was looking them up the other night with a view of fitting one to the Stag as they would make tuning those carbs soooo easy.

                          Innovate kit is around $220 over here., hardest bit is welding a plug into the exhaust.
                          Last edited by trunt; 14th February 2018, 03:19.
                          Terry Hunt, Wilmington Delaware

                          www.terryhunt.co.uk

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