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  • Backfire at idle

    Alright everybody my bike backfires when idling and at low RPMs. Also I hear a pop coming from the carbs every so often. I know the popping is from the carbs because it blew a cap off of one of the carb boots. What is the first thing I should do to try to find the cause. The carbs are synced, at least they where about 1000 miles ago.
    USMC 2005 - Present

    79 XS1100F -Mileage unknown - Clubman bars, aftermarket headlight and speedometer, 4 into 1 straight through exhaust, TopCat's fuse box, 1980G rear fender - Daily driver - My first Motorcycle
    78 XS1100E - Rebuilt And Sold I SHOULD OF KEPT IT!!!

  • #2
    Carbs

    1st, I just went through the same thing, It is most likely, carbs. The jets and ports on these are so small that any thing can cause a problem. Make sure that you remove the emulsion tubes (missed one on mine and POP POP POP Next, the wasted spark system can blow an air filter off, if all is not running right with the carbs, so start with the carbs, they can be a PITA on these bikes, and thanks for your service Marine


    Originally posted by mmaddix View Post
    Alright everybody my bike backfires when idling and at low RPMs. Also I hear a pop coming from the carbs every so often. I know the popping is from the carbs because it blew a cap off of one of the carb boots. What is the first thing I should do to try to find the cause. The carbs are synced, at least they where about 1000 miles ago.
    1979 XS1100 Special (Mad Max, OEM) Current
    1980 XS1100 Special
    1990 V Max
    1982 KZ750 LTD Twin
    1986 700 FZR Yamaha Fazer (faster then expected)
    1979 XS750 Special (my 1st Special)
    1974 CB750-Four



    Past/pres Car's
    1961 Catalina 389/1970 Torino GT 351/1967GTO 12to1 comp./ Roller cam/ T-10/ 456 gear/Tri-power/1967 GTO 400, 1969 Camaro, 1968 Z28, 2001 BMW M Roadster 0 to 60 in 4.5 sec. Jaguar XK8

    Comment


    • #3
      Check your valves, a too-tight valve can cause backfiring issues. Look at your cam timing while you're in there. But OEM is probably right, you'll need to pull the carbs and go through them, these things can plug up at the drop of a hat...
      Fast, Cheap, Reliable... Pick any two

      '78E original owner - resto project
      '78E ???? owner - Modder project FJ forks, 4-piston calipers F/R, 160/80-16 rear tire
      '82 XJ rebuild project
      '80SG restified, red SOLD
      '79F parts...
      '81H more parts...

      Other current bikes:
      '93 XL1200 Anniversary Sportster 85RWHP
      '86 XL883/1200 Chopper
      '82 XL1000 w/1450cc Buell, Baker 6-speed, in-progress project
      Cage: '13 Mustang GT/CS with a few 'custom' touches
      Yep, can't leave nuthin' alone...

      Comment


      • #4
        Originally posted by XS1100_OEM4ME View Post
        and thanks for your service Marine
        I guess I will pull the carbs and clean them and see how everything goes after that. And thank you for your support, it is well appreciated.

        Originally posted by crazy steve View Post
        Check your valves, a too-tight valve can cause backfiring issues. Look at your cam timing while you're in there.
        I will check the valves and cam timing. I wanted to anyways and now I have a reason.

        Thanks again fellow members.
        USMC 2005 - Present

        79 XS1100F -Mileage unknown - Clubman bars, aftermarket headlight and speedometer, 4 into 1 straight through exhaust, TopCat's fuse box, 1980G rear fender - Daily driver - My first Motorcycle
        78 XS1100E - Rebuilt And Sold I SHOULD OF KEPT IT!!!

        Comment


        • #5
          This might be helpful
          http://www.zrxoa.org/forums/showthre...an-carbs-(PICS
          Not all carbs are the same, but they all need cleaned to the complet degree
          1979 XS1100 Special (Mad Max, OEM) Current
          1980 XS1100 Special
          1990 V Max
          1982 KZ750 LTD Twin
          1986 700 FZR Yamaha Fazer (faster then expected)
          1979 XS750 Special (my 1st Special)
          1974 CB750-Four



          Past/pres Car's
          1961 Catalina 389/1970 Torino GT 351/1967GTO 12to1 comp./ Roller cam/ T-10/ 456 gear/Tri-power/1967 GTO 400, 1969 Camaro, 1968 Z28, 2001 BMW M Roadster 0 to 60 in 4.5 sec. Jaguar XK8

          Comment


          • #6
            For help cleaning the carbs, look up the thread titled "Carb Cleaning 101" by Wildkat.

            Tuning, meaning a lean condition can also cause the popping your describing as well. So it coul dbe as simple as another 1/4 turn or so on the mixture screws.
            Life is what happens while your planning everything else!

            When your work speaks for itself, don't interrupt.

            81 XS1100 Special - Humpty Dumpty
            80 XS1100 Special - Project Resurrection


            Previously owned
            93 GSX600F
            80 XS1100 Special - Ruby
            81 XS1100 Special
            81 CB750 C
            80 CB750 C
            78 XS750

            Comment


            • #7
              So when I pull the carbs to clean them I want to make sure I have the correct jets and everything in them. Which main and other jets (I forget the name of them I think they are pilot jets) should I have in there? I am ruining air pods without the airbox and I have 4 into 1 exhaust with a completely gutted muffler, nothing at all on the inside of the muffler. Is there anything else that should be checked to see if the correct size is in there for my setup?
              USMC 2005 - Present

              79 XS1100F -Mileage unknown - Clubman bars, aftermarket headlight and speedometer, 4 into 1 straight through exhaust, TopCat's fuse box, 1980G rear fender - Daily driver - My first Motorcycle
              78 XS1100E - Rebuilt And Sold I SHOULD OF KEPT IT!!!

              Comment


              • #8
                Well, now another light is shown on the subject. What you have is commonly referred to as straight or open exhaust, meaning no baffling for back pressure.

                When you jet the carbs, you do need to account for changes from factory set up like the POD filters your using, and the non stock exhaust. There is a thread on here, some where I do not recall right off, on how to select the jetting based upon the year of the carbs, and the options you have for intake and exhaust.

                I will add that very few folks have ever found success tuning for open exhaust like yours. It definitely causes a lean condition at idle and will tend to pop on decel and pop or backfire at idle.

                Depending who made the exhaust your running, you may be able to get some baffling for it, like a Supertrap insert.
                Life is what happens while your planning everything else!

                When your work speaks for itself, don't interrupt.

                81 XS1100 Special - Humpty Dumpty
                80 XS1100 Special - Project Resurrection


                Previously owned
                93 GSX600F
                80 XS1100 Special - Ruby
                81 XS1100 Special
                81 CB750 C
                80 CB750 C
                78 XS750

                Comment


                • #9
                  It was doing the same thing when I had a baffle in there. The whole reason why its Ann open exhaust is because it back fired so hard one time it blew the baffle and the end cap out of the muffler
                  USMC 2005 - Present

                  79 XS1100F -Mileage unknown - Clubman bars, aftermarket headlight and speedometer, 4 into 1 straight through exhaust, TopCat's fuse box, 1980G rear fender - Daily driver - My first Motorcycle
                  78 XS1100E - Rebuilt And Sold I SHOULD OF KEPT IT!!!

                  Comment


                  • #10
                    Jetting

                    I think this is what your looking for.

                    Jetting guide...

                    http://www.xs11.com/forum/showthread.php?t=382
                    mack
                    79 XS 1100 SF Special
                    HERMES
                    original owner
                    http://i946.photobucket.com/albums/a...ps6932d5df.jpg

                    81 XS 1100 LH MNS
                    SPICA
                    http://i946.photobucket.com/albums/ad305/mack-055/2.jpg

                    78 XS 11E
                    IOTA
                    https://youtu.be/wB5Jfbp6SUc
                    https://youtu.be/RaI3WYHSuWA



                    Have recovery trailer and shop if you breakdown in my area.
                    Frankford, Ont, Canada
                    613-398-6186

                    Comment


                    • #11
                      Exaust

                      Well, with "0" back presure, you got a challange on your hands, not saying it cant be done, just very hard to get it to run right that way. If you can mod it to have a super trap kinda end on the exaust pip, you can add baffels as needed till you get it running just right IMHO. Like these:

                      http://www.ebay.com/itm/SUPERTRAPP-4...sories&vxp=mtr

                      http://www.ebay.com/itm/SUPERTRAPP-4...sories&vxp=mtr

                      Originally posted by mmaddix View Post
                      It was doing the same thing when I had a baffle in there. The whole reason why its Ann open exhaust is because it back fired so hard one time it blew the baffle and the end cap out of the muffler
                      1979 XS1100 Special (Mad Max, OEM) Current
                      1980 XS1100 Special
                      1990 V Max
                      1982 KZ750 LTD Twin
                      1986 700 FZR Yamaha Fazer (faster then expected)
                      1979 XS750 Special (my 1st Special)
                      1974 CB750-Four



                      Past/pres Car's
                      1961 Catalina 389/1970 Torino GT 351/1967GTO 12to1 comp./ Roller cam/ T-10/ 456 gear/Tri-power/1967 GTO 400, 1969 Camaro, 1968 Z28, 2001 BMW M Roadster 0 to 60 in 4.5 sec. Jaguar XK8

                      Comment


                      • #12
                        Originally posted by mmaddix View Post
                        with a completely gutted muffler, nothing at all on the inside of the muffler. Is there anything else that should be checked to see if the correct size is in there for my setup?
                        A gutted muffler can giv you fits. Sometimes there is nothing that can be done with carb adjustments to compensate. You are fighting an echo pressure wave at certain RPMS that interfere with exhausting from a cylinder. I would suggest that you get a muffler that has a descent baffle in it. THEN adjust the carbs, otherwise you might have to pull the carbs countless times for nothing!
                        Skids (Sid Hansen)

                        Down to one 1978 E. Stock air box with K&N filter, 81H pipes and carbs, 8500 feet elevation.

                        Comment


                        • #13
                          PS, backfiring like that is a fire risk and it will turn your affected carb black.
                          Skids (Sid Hansen)

                          Down to one 1978 E. Stock air box with K&N filter, 81H pipes and carbs, 8500 feet elevation.

                          Comment

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