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  • Carb Question

    I picked up a 78 XS a couple weeks ago at quite a bargain. My other bikes include a 80 XS Special and an 82 XJ1100. The previous owner had a local mechanic do some work to the bike, including some carb work and putting a lined XS Special tank on what I am fairly certain is a standard XS. The bike cranked up--compression was a bit low, but all 4 cylinders were within 5-8% of each other--around 115-120 psi. The bike would only run on choke and 2 of the cylinders were not firing, and shortly, there was fuel coming out of the air filter. So, I pulled the carbs to begin cleaning them. In breaking down the carbs, it was obvious some work had been done. The main jets, and the pilot jets are new. But--The carb closest to the choke slide is different than the other 3 carbs. I have no experience with 78 model bikes, so I didn't know if this was normal or not, or if it even makes a difference.

    Any input would be great. Thanks!



    Last edited by Edisto; 02-17-2011, 10:02 AM.
    1979 XS1100 F
    1980 XS1100 Special--Frankenstein
    1982 XJ1100 Maxium x 2
    1980 Honda CB 900
    1981 Honda CB 900
    1981 Honda CB650x2
    2003 Honda 1300 VTX Retro-sold

  • #2
    The right one in the pic i am fairly certain (never actually seen one personally) is the late model carb and the left one is the regular early model carb. They don't mix well and you need to jet the different model carbs.differently. you would need to find a replacement carb body to match the other 3 for that carb in that position on the rack.
    Nathan
    KD9ARL

    μολὼν λαβέ

    1978 XS1100E
    K&N Filter
    #45 pilot Jet, #137.5 Main Jet
    OEM Exhaust
    ATK Fork Brace
    LED Dash lights
    Ammeter, Oil Pressure, Oil Temp, and Volt Meters

    Green Monster Coils
    SS Brake Lines
    Vision 550 Auto Tensioner

    In any moment of decision the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.

    Theodore Roosevelt

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    • #3
      Looks like you have an 80 or newer carb body bolted in to the 78 carb rack there. I would look to ebay to get a good complete rack.
      Ty

      78 XS1100E - Now in Minnesota
      80 XS1100LG - The Punisher
      82 XJ1100 - Current project - The Twins
      82 XJ1100 - Wife's Bike - The Twins
      82 XJ1100 - Daughter's Bike
      72 Suzuki TS125 - Daughter's Bike
      72 Yamaha Mini JT2 - Youngest Daughter's bike (She wants a bigger one now)

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      • #4
        The carb on the right is a '80-81 type, while the other is original '78-79. You'll need to find a replacement, as these two types jet and tune quite differently. All one type or the other is OK, but mixed is a no-no...
        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...

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        • #5
          Thanks guys! I have another set of carbs I can put on this bike to at least let me see if there is anything else wrong with her before I spend $$ on more parts.
          1979 XS1100 F
          1980 XS1100 Special--Frankenstein
          1982 XJ1100 Maxium x 2
          1980 Honda CB 900
          1981 Honda CB 900
          1981 Honda CB650x2
          2003 Honda 1300 VTX Retro-sold

          Comment


          • #6
            Yep you decisively have a mix and match set of carb bodies there. The number one is from an 80-81 set. the other three are 78-79 models. The screw hole off to the side of the float needle seat hole is for the retainer that holds that seat in place on the later style. The older ones, that seat screws in.

            I'm not sure why it would not work like that if jetted properly to be honest since they are individual to each cylinder, and you can put the ful bank of 80-81 carbs on any year XS and they will run fine. I've heard others state the combo does not work out well though.

            The 80-81 carbs do get jetted substantially different though.
            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

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            • #7
              I thought the mechanic that did the work screwed the pooch. The fuel lines were a mess, the inside of the tank was poorly done, and now this. Now, I really feel bad for the guy I bought it from.
              1979 XS1100 F
              1980 XS1100 Special--Frankenstein
              1982 XJ1100 Maxium x 2
              1980 Honda CB 900
              1981 Honda CB 900
              1981 Honda CB650x2
              2003 Honda 1300 VTX Retro-sold

              Comment


              • #8
                Originally posted by DGXSER View Post
                I'm not sure why it would not work like that if jetted properly to be honest since they are individual to each cylinder, and you can put the ful bank of 80-81 carbs on any year XS and they will run fine. I've heard others state the combo does not work out well though.
                I think the big problem is the slide size difference. The later carbs have larger slides and different slide springs, so don't 'react' the same as the early units. This is fine as long as all carbs match, but with a oddball in there I would think that getting fuel curves to match at various rpms/loads would be extremely hard. The float bowl venting is another difference (I wonder how that was addressed with this combo?).

                Whatever you do, it's important that parts match. While you can swap some parts between the early/late carbs (the later plastic floats into the early carbs is a common swap), for any individual part they should all be the same.
                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


                • #9
                  I'll have to agree with Steve. The characteristics of the carbs once off idle are different, and they tuned up differently. As was said, you can change the whole bank to either one, but you can't mix them. From what I have seen with them on other models, the mixture and airflow characteristics in the midrange are quite a bit different.
                  Cy

                  1980 XS1100G (Brutus) w/81H Engine
                  Duplicolor Mirage Paint Job (Purple/Green)
                  Vetter Windjammer IV
                  Vetter hard bags & Trunk
                  OEM Luggage Rack
                  Jardine Spaghetti 4-2 exhaust system
                  Spade Fuse Box
                  Turn Signal Auto Cancel Mod
                  750 FD Mod
                  TC Spin on Oil Filter Adapter (temp removed)
                  XJ1100 Front Footpegs
                  XJ1100 Shocks

                  I was always taught to respect my elders, but it keeps getting harder to find one.

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