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    Stromberg carbs question advice

    I had a leak on the choke on one carb so I removed them and repaired the choke/cold start assemblies and the by pass valve assemblies(which were not even functioning) removed the float chamber and cleaned out the carb body replaced the seals on the throttle spindles and assembled. Since the car had been sitting i thought that would get me started and back on the road. I went to set the cabs up and with the linkage arms removed started setting the idle at 800 to 850 rpm. It would then start to creep up in revs, I then pulled the cap dampner assembly and pushed it inwards and this would bring the revs back down but this would repeat the dampner would start to lift and revs go up.After a lot of trying it repeated so I have come to the conclusion that the diaphragm is at fault and needs replaced. All the other bit and bobs are good needle valves good float good no sticky bits on the dampner so I am just looking for confirmation that I am going in the right direction. Sadly no driving this week end.
    Stuart

    #2
    unable to bring the revs down can be due to torn diaphragms in the by pass valves. fitted to Fed cars. I had this problem. some are adjustable others fixed. I can remember they type my car had. but after replacement revs behaved normal

    Comment


      #3
      I serviced both the by pass and the choke or cold start assemblies waiting on the diaphragms. The by pass valve on both carbs did not work but the car would run the fuel leak started me going through the carbs. Will post result. Thanks

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        #4
        I have just replaced the diaphragms on both carbs and also the small O ring on the metering needle assembly where it goes into the air valve. Refurbished the choke and by pass valves and new seals on the spindles also checked the temp compensators. Started the engine and it runs fine with the exception of I cannot get the rpm to set at slow idle. I have the throttle cable and choke cables and kick down disconnected. The air valve wants to rise up the dampner pots were filled with oil and when running if I push down on them they will slow the revs. Can the air valve return springs give out after time.? I am going to pull the air valve metering assy back apart and recheck that. If the o ring is not sealing then the oik will leak that is the only way it can ? yes or no ! Any help advice.

        Thanks Stuart

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          #5
          I need some help, I fitted the carbs back with new springs diaphragms went through the temp compensators and air by pass valves which are US only as I understand checked the floats needle valves etc. Trying to set the idle speed which I can get to but the carb air valve wants to lift up and the revs go up. The dampners have new o rings and filled with oil. At this stage the carbs do not have the linkage connected I am just trying to get it to idle at 800 to 850. When I started it today it did idle then after it warmed up the engine revs crept up it seemed it was the right hand carb that was lifting I would remove the dampner and push the air valve back down and get it to go back to normal this repeated serveral times. Can anyone help I must be missing something I need to be driving this car.

          Thanks Stuart

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            #6
            Did you adjust the bypass valves?? if they are floating that would force the rpm up..

            http://www.buckeyetriumphs.org/techn...I/CarbsIII.htm

            Terry
            Terry Hunt, Wilmington Delaware

            www.terryhunt.co.uk

            Comment


              #7
              I did not adjust them they apparently were not working before, when I opened them up the diaphagm was in bits and the seating surface was pitted. I cut the seating surface with emery paper and had it sealing but never adjusted them.I will revisit that.I have the information you posted and thanks for advice it's a bugger when you get into this and try to find the solution.

              Stuart

              Comment


                #8
                My '71 Stga were fitted with '73 carbs which had the by pass valves.
                I had the same symptoms of unable to keep the revs down
                I did replace the diaphragms in the bypass valves. I don't recall making any adjustments, ISTR there are two types, one adjustable the other not. Mine are adjustable.

                Anyway the replacement of them resolved the idle problem.

                I now have a set of carbs from a UK stag .( I wanted an advance port) The set I have does not have this bypass.

                If you want to fit vacuum advance, there is an outfit int he US that can drill and tap a hole in the right hand carb.

                Sujit,

                Cupertino, CA





                Comment


                  #9
                  I have removed the bypass valves and am checking them for function also going to make cover plates to replace them while I set the idle, more to follow.

                  Comment


                    #10
                    Just a small update on a from a very frustrated owner, I had the carbs on and off numerous times and found that the right hand carb air piston was hanging up in the top of the housing/ cover. I fixed that and removed the by pass valves which I think are for Federal cars and put tape over the openings. I also replaced the rod ends with metal ones the plastic one are a pain. Got the car running and the carbs dialed in both breathing about the same and got the idle set. I rechecked / overhauled the by pass valves and had them set the same put them back on the carbs and fitted the carbs back on the car.It was late and I was tired I packed it in for the night. Next day I thought I would check the running speed of course I forgot that I had disconnected and plugged the fuel line last night.The car started an ran then cut out as you would when you have no fuel. When I remembered about the fuel line and connected it nothing no fuel. This was an electric pump just installed so I thought I screwed it up and fitted the old pump and got it running and then quit while I was ahead. A week passes and I go out last Sunday and think I can set the linkage and fit the throttle cable and drive it around the block at least, I get it out into the street and it starts dying on me cus the fuel pump packed it in no fuel, changed it out to the electric which I had bench tested and got it running and back into the garage where it sits. I had to walk away and if you walked by and made an offer just then I most likely would have said yes. There it sits when I might get to it this week end really annoying.

                    Comment


                      #11
                      I would be very certain frustration wise, most of us have been there!
                      Often when I have to walk away and come back I find I see the problem from a fresh new angle..
                      Stag 2500S
                      Jaguar STypeR Citroen C5

                      Comment


                        #12
                        Sit down, have a beer, then remember that you really want a Stag and have no intention of selling it!! Ever !!!
                        Then convince yourself that a simple piece of machinery cannot defeat human ingenuity, and try to follow the symptoms logically.

                        Clearly both pumps can work.

                        So, either it is an electrical supply problem - usual culprit is the inertia switch, but after 40+ years, any part of the electrical supply could have a dirty/loose joint. Can you hear the pump ticking? Perhaps check the connectors to the pump itself, because each time you disturb these, it works for a while.
                        Or, there is some dirt blocking the fuel supply somewhere (pick-up in the tank, or in a pipe somewhere). Again, obvious first place to look is around the pump, because when you disturb the pump, it works for a while.
                        Final thought - is the tank venting correctly, or are you creating a vacuum? However, I would have thought you would have to draw off a lot of fuel to experience this effect.
                        '72 Manual O/d Saffron Yellow

                        Comment


                          #13
                          I think it could be a voltage drop the pumps were going just not getting the fuel out. Anyway you are all correct walk away and take a break. I will try again this week end. Going to get some petrol or gas as they say here and run the pump into a gallon container and see how that works. I will check the voltage last time it was,11 so that should be good. Once I get it running all this will be a distant memory.

                          Comment


                            #14
                            It has been a journey but with some time to play with the carbs I found on one carb the air valve hanging up ever so slightly in the top of the carb cover have installed the electric pump back in both carbs are almost dialed in sync just have to fit the elbows filter etc and see how it runs. Great learning curve but it did test me. Might even get it running well this week end.
                            Last edited by elvimto; 6th December 2018, 06:28.

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