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  • #1

    79 carbs

    Took my carbs of for a pre-rally cleaning and to investigate why it was running so rich and getting poor mileage.

    A little history on these carbs. They were given to me by a friend, i put them on the bike, quick sync and they ran good so I never even pulled the bowls off. Rode it primarily around town with it, runs good and strong. When i rode it to the Colorado rally, i was only getting between 21 and 26 mpg. This bike had always gotten between 32 and 36 with the 80 carbs I had been running on it.

    The bike is a 79, so I wanted to switch back to the appropriate carbs. I think I found one reason it is running so rich, two of the idle mixture screws had been broken off, and then the screws had been turned on a lathe to make them work. (at least thats the way it looks.) While it runs nice and strong that way, it may be dumping too much fuel. Also, there is not washer and o-ring on the idle mixture screws. Are 79's supposed to have them?

    Another oddity, the emulsion tubes are different? The holes are not the same. 2 have a series of 4 holes in a row on 4 sides. The other two have a different pattern. Is this normal on the 79? If so, which carbs get which?


    Harry

    The voices in my head are giving me the silent treatment.

    '79 Standard
    '82 XJ1100
    '84 FJ1100


    Acta Non Verba
    Tags: None
  • #2
    No O-rings on the mixture screws Harry. The needle jets with the fewer holes go in the #2 & #3 carbs.

    I have a really easy way to get those broken tips out and I think I might have a couple of good screws. I'll look.

    I've come to the conclusion that when these bikes are running right they get lousy mileage. You and I got approximately the same on the Colorado trip.

    these are the brand new before Colorado Mac pipes after the trip. They are almost perfect looking. Maybe even a touch lean.




    you ever going to send those keys for the Vetter bags?
    Greg

    Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”

    ― Albert Einstein

    80 SG Ol' Okie;79 engine & carbs w/pods, 45 pilots, 140 mains, Custom Mac 4 into 2 exhaust, ACCT,XS850 final drive,110/90/19 front tire,TKat fork brace, XS750 140 MPH speedometer, Vetter IV fairing, aftermarket hard bags and trunk, LG high back seat, XJ rear shocks.

    The list changes.

    Comment

    • #3
      Sorry Greg, you gonna make the trip? Could just bring them with me. If not, i will get them in the mail to ya. The holes are clear, looks like Bob just didn't wanna buy new screws. I remember him talking about turning them on his lathe once, I guess these are the ones he was talking about. And this same bike with 1980 carbs on it got over 10mpg better. Same type of riding and riding style. I can't believe that it would be that much of a difference. If these emulsion tubes are correct, then I don't need new ones, just need a couple idle mixture screws.

      As you saw in Colorado, I was running too rich. Supertrapp exhaust with pod filters. Ran great until I put these carbs on, then had a stumble from 3-4k rpm. hit 4500 and it would take off. Got much worse when we hit elevation in Colorado. Sooooo, I opened the exhaust up (took the end caps off of the supertrapp and basically made it an open pipe) and it ran much better. I think this helped lean it out. Back down at lower elevation, the stumble is gone.... but anyone riding behind me will be bleeding from the ears before long. It sounds good but WAY too loud. Now i know what a harley rider feels like, don't really like it.

      So, my plan is to fix the idle mixture screws, see if that gets it back to where it wants to be, then maybe go with smaller pilots since the problem seems to be too rich at lower rpms when I should be still running on the pilots. Is my thinking here flawed? Ideas and opinions are welcome.
      Harry

      The voices in my head are giving me the silent treatment.

      '79 Standard
      '82 XJ1100
      '84 FJ1100


      Acta Non Verba

      Comment

      • #4
        Greg

        Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”

        ― Albert Einstein

        80 SG Ol' Okie;79 engine & carbs w/pods, 45 pilots, 140 mains, Custom Mac 4 into 2 exhaust, ACCT,XS850 final drive,110/90/19 front tire,TKat fork brace, XS750 140 MPH speedometer, Vetter IV fairing, aftermarket hard bags and trunk, LG high back seat, XJ rear shocks.

        The list changes.

        Comment

        • #5
          Yep, those are what I need. Will give you a call in a few min.
          Harry

          The voices in my head are giving me the silent treatment.

          '79 Standard
          '82 XJ1100
          '84 FJ1100


          Acta Non Verba

          Comment

          • #6
            Check the needle setting and the main jets. The snap ring on the main needles should be in the middle slot out of 5. The mains I would use 142.5 across all 4 AT THE LARGEST, with a 45 pilot jet. Properly synced, that should give you good performance and your mileage back.
            Ray Matteis
            KE6NHG
            XS1100 E '78 (winter project)
            XS1100 SF Bob Jones worked on it!

            Comment

            • #7
              Originally posted by Bigfoot View Post
              Sorry Greg, you gonna make the trip? Could just bring them with me. If not, i will get them in the mail to ya. The holes are clear, looks like Bob just didn't wanna buy new screws. I remember him talking about turning them on his lathe once, I guess these are the ones he was talking about. And this same bike with 1980 carbs on it got over 10mpg better. Same type of riding and riding style. I can't believe that it would be that much of a difference. If these emulsion tubes are correct, then I don't need new ones, just need a couple idle mixture screws.

              As you saw in Colorado, I was running too rich. Supertrapp exhaust with pod filters. Ran great until I put these carbs on, then had a stumble from 3-4k rpm. hit 4500 and it would take off. Got much worse when we hit elevation in Colorado. Sooooo, I opened the exhaust up (took the end caps off of the supertrapp and basically made it an open pipe) and it ran much better. I think this helped lean it out. Back down at lower elevation, the stumble is gone.... but anyone riding behind me will be bleeding from the ears before long. It sounds good but WAY too loud. Now i know what a harley rider feels like, don't really like it.

              So, my plan is to fix the idle mixture screws, see if that gets it back to where it wants to be, then maybe go with smaller pilots since the problem seems to be too rich at lower rpms when I should be still running on the pilots. Is my thinking here flawed? Ideas and opinions are welcome.
              I had that same stumble FOREVER with this 79 engine until I opened up the exhaust too.

              I think the later carbs run too lean. (Ralph Nader) Even my original 80 engine ran better with the early carbs on it.

              I actually went up 1 size on the pilots and the mains with mine. Got much better low end throttle response. I can really tell the difference if I put the 42.5s back in as I did when I was searching for the loss of power issue.

              Look at the pilot on an XJ, it calls for a 47.5 pilot. same mains, same needles and same needle jets as the late XS carbs.
              Greg

              Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”

              ― Albert Einstein

              80 SG Ol' Okie;79 engine & carbs w/pods, 45 pilots, 140 mains, Custom Mac 4 into 2 exhaust, ACCT,XS850 final drive,110/90/19 front tire,TKat fork brace, XS750 140 MPH speedometer, Vetter IV fairing, aftermarket hard bags and trunk, LG high back seat, XJ rear shocks.

              The list changes.

              Comment

              • #8
                I put everything back together and the floats were way off, which is I am sure what was causing my issues in the first place. On a 79 they should be set at 25.7 mm according to what i read. These were closer to 20-22.
                Harry

                The voices in my head are giving me the silent treatment.

                '79 Standard
                '82 XJ1100
                '84 FJ1100


                Acta Non Verba

                Comment

                • #9
                  Yeah, that would cause a problem! The BIG thing is they all 4 NEED to be the SAME!! Out here, with the junk they call gas, I set mine to about 22 to get it running almost correctly. I HATE California gas!
                  Ray Matteis
                  KE6NHG
                  XS1100 E '78 (winter project)
                  XS1100 SF Bob Jones worked on it!

                  Comment

                  • #10
                    Put the carbs back on the bike today with the floats adjusted properly. Synced them properly and took it for a ride. Bike is running great again through the entire RPM range, low end stumble is gone. This 79 has always been the quickest XS I have ridden and it is back to where it was before I swapped carbs.
                    Harry

                    The voices in my head are giving me the silent treatment.

                    '79 Standard
                    '82 XJ1100
                    '84 FJ1100


                    Acta Non Verba

                    Comment

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