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  • Gas in airbox, petcock OK

    My brother in law and I are working on our first restoration, a 1978 XS1100 bought from original owner with 30k miles. It had been sitting for 14 years and wasn't running. Rebuilt carbs and petcock, changed plugs and did a few other things. It runs now but after riding and sitting overnight there was gas in the airbox. I checked both petcocks and they do not leak gas when in the "ON" position. So I tried to see if one or more of the carbs was leaking by taking the airbox off, and putting both petcocks in "PRI". Thinking that if a float was stuck that carb would leak, but nothing leaked. Would like to try and figure out what carb is leaking before taking them off. Any suggestions how to determine that? One thing to note, the airbox looks like it had some melting at one point (from before we bought it). Does it need to be replaced? Could it be part of the problem?

    Thanks in advance
    Steve

    Click image for larger version

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  • #2
    Had that happen to me when I was riding around town. Smelled gas and looked down and there was gas pouring out of the airbox drain. All it takes is any restriction in the needle valve movement, condition of needle valve or a sticky float. I would suggest pulling off the float bowls, having a closer look at the needle valve seats and making sure everything is clean, clean, clean and moving freely. Internal air pressures may also have an effect on when you notice the leakage - running: yes, stopped: no. Happened to me when the bike was fairly new - turned out to be a small piece of plastic causing a needle valve to stick - at least I had an AHA! moment and problem didn't remain a mystery.
    Own - 1980 XS1100G (one owner-me)
    Owned - 1976 XS750D
    Owned - (unknown year) XS650
    (+ too many Yammies/Hondas to mention)

    Comment


    • #3
      The float valve seats need polished and rubber tips of the float valves need inspected. I use a qtip on a drill with a touch (just enough to dampen the cotton) of aluminum polish, then run some dry ones to clean out the polish. Make sure the hangers for the valves are in the proper position, it makes a difference.

      Once they are cleaned set the float height and fill the carbs on the bench to make sure nothing is weeping.
      1979 XS1100 Special
      1980 XS1100 Std parts bucket
      1987 ZL1000 Eliminator
      1976 XS750D Project in waiting

      Comment


      • #4
        I would look for an airbox from andreashweiss. He has a lot of parts for our bikes. The rebuild kit for the petcocks may not be stopping the fuel as it needs to. Some of the kits don't quite seal, and they will dribble a little. The big thing is the carbs. You will need to pull them and check floats again. I usually put then in a vise upside down with the bowls off to verify they will shut off. Also, check the float gasket and make sure it's not hanging up.
        Here is a good place to start if you have not read this: https://xs11.club/forum/repairs/carburetors-fuel-system-aa
        One last thing you can do. Remove the switch fro
        m the petcock, and file/grind the tang off the inside of the chrome bit that holds it in place. This will allow you to turn the selector up, and you now have a positive off position.
        Ray Matteis
        KE6NHG
        XS1100 E '78 (winter project)
        XS1100 SF Bob Jones worked on it!

        Comment


        • #5
          Originally posted by LenB View Post
          Had that happen to me when I was riding around town. Smelled gas and looked down and there was gas pouring out of the airbox drain. All it takes is any restriction in the needle valve movement, condition of needle valve or a sticky float. I would suggest pulling off the float bowls, having a closer look at the needle valve seats and making sure everything is clean, clean, clean and moving freely. Internal air pressures may also have an effect on when you notice the leakage - running: yes, stopped: no. Happened to me when the bike was fairly new - turned out to be a small piece of plastic causing a needle valve to stick - at least I had an AHA! moment and problem didn't remain a mystery.
          Yea, I think mine are only leaking when the bike is running though I haven't had it happen when I had it running but just on its stand. So far, it only happen (twice) after a short ride. I was initially under the impression that you need to have both petcock and carb fail to get leakage but I believe now that only applies for when the bike is not running.

          Comment


          • #6
            Originally posted by DiverRay View Post
            I would look for an airbox from andreashweiss. He has a lot of parts for our bikes. The rebuild kit for the petcocks may not be stopping the fuel as it needs to. Some of the kits don't quite seal, and they will dribble a little. The big thing is the carbs. You will need to pull them and check floats again. I usually put then in a vise upside down with the bowls off to verify they will shut off. Also, check the float gasket and make sure it's not hanging up.
            Here is a good place to start if you have not read this: https://xs11.club/forum/repairs/carburetors-fuel-system-aa
            One last thing you can do. Remove the switch fro
            m the petcock, and file/grind the tang off the inside of the chrome bit that holds it in place. This will allow you to turn the selector up, and you now have a positive off position.
            Thanks, I'll check out andreashweiss. Do you think my airbox could be part of the issue?

            Comment


            • #7
              Not if the bike is running well, but it's still got problems. The '78 uses the airbox for clean vent air to the carbs. If the vents are plugged, you can have both not running well and flooding. Your airbox had a backfire and then flames from looking at it.
              Ray Matteis
              KE6NHG
              XS1100 E '78 (winter project)
              XS1100 SF Bob Jones worked on it!

              Comment


              • #8
                Originally posted by 2WheelFun View Post
                The float valve seats need polished and rubber tips of the float valves need inspected. I use a qtip on a drill with a touch (just enough to dampen the cotton) of aluminum polish, then run some dry ones to clean out the polish. Make sure the hangers for the valves are in the proper position, it makes a difference.

                Once they are cleaned set the float height and fill the carbs on the bench to make sure nothing is weeping.
                If the carbs you have are the original from a 78 and it sounds like they are then your float valve needles don't have rubber tips. They are solid metal and seal against the brass base of the seat. You did not indicate what all you have done on the carbs. Did you completely disassemble them to clean. Meaning were the float pins removed so you had full access to the needle valves and seats? If not then that area of the carbs remains suspect. If you have and everything is clean and working correctly then maybe the bowl gaskets are interfering with the floats. The airbox serves as the vent for the carbs and with the damage shown in the pictures then it is possibly causing a venting issue. Definitely look for a replacement. The later airboxes did not vent through the airbox so you will need one from either a 78 or 79 standard. Some of the 79's did not vent either so I would concentrate on a 78.
                2 - 80 LGs bought one new
                81 LH
                02 FXSTB Nighttrain
                Jim

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                • #9
                  Thanks for the clarification, I thought they would be like my Keihin on my Kaw. Either way those seats and valves need a good cleaning to have them seal properly.
                  1979 XS1100 Special
                  1980 XS1100 Std parts bucket
                  1987 ZL1000 Eliminator
                  1976 XS750D Project in waiting

                  Comment


                  • #10
                    Originally posted by cajun31 View Post

                    If the carbs you have are the original from a 78 and it sounds like they are then your float valve needles don't have rubber tips. They are solid metal and seal against the brass base of the seat. You did not indicate what all you have done on the carbs. Did you completely disassemble them to clean. Meaning were the float pins removed so you had full access to the needle valves and seats? If not then that area of the carbs remains suspect. If you have and everything is clean and working correctly then maybe the bowl gaskets are interfering with the floats. The airbox serves as the vent for the carbs and with the damage shown in the pictures then it is possibly causing a venting issue. Definitely look for a replacement. The later airboxes did not vent through the airbox so you will need one from either a 78 or 79 standard. Some of the 79's did not vent either so I would concentrate on a 78.
                    The carbs are original. They were completely disassembled. Used the carb rebuild kit from Dennis Kirk (link below) as well put in new floats. I'm pretty new to this so not sure I fully understand the carb/airbox/venting relationship so will need to read up on that some more. At this point I'm pretty sure the carbs don't leak when just sitting there but not sure if it is leaking while I am riding it or just after I come back. I had done a quick ride with no airbox and didn't see any leakage afterwards. But maybe didn't ride for long enough, or maybe the airbox is the culprit. I will pull the carbs this weekend and check them all.

                    Thanks!
                    Steve

                    https://www.denniskirk.com/k-and-l/c...prd/170965.sku

                    Comment


                    • #11
                      The carbs are original. They were completely disassembled. Used the carb rebuild kit from Dennis Kirk (link below)
                      I hope you did NOT use the needle and jets!!!! They are the wrong parts. If it's not Mikuni, you will have problems trying to tune the carbs. The float needle and seat usually work OK, but everything else is suspect. At 30K on the bike, you should be able to clean and reuse the jets and just replace the needle/seats and gaskets with the new parts.
                      Ray Matteis
                      KE6NHG
                      XS1100 E '78 (winter project)
                      XS1100 SF Bob Jones worked on it!

                      Comment


                      • #12
                        Originally posted by DiverRay View Post
                        I hope you did NOT use the needle and jets!!!! They are the wrong parts. If it's not Mikuni, you will have problems trying to tune the carbs. The float needle and seat usually work OK, but everything else is suspect. At 30K on the bike, you should be able to clean and reuse the jets and just replace the needle/seats and gaskets with the new parts.
                        I did use the needle and jets. :-(

                        They seemed very similar/the same as the originals. The bike does run pretty well, idles around 1000 once warmed up, and was able to sync the carbs pretty close. Maybe the kit has improved over the years? Fortunately we did save all the original parts so I can put them back in if need be. Wasn't aware there was an issue.

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                        • #13
                          Probably a dumb question but the part in my air cleaner that is messed up (part 28) what exactly does it do? If I remove it what would happen?

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                          • #14
                            The crankcase vent hose hooks up to that. #44 in this picture
                            Last edited by cajun31; 04-27-2021, 08:39 AM.
                            2 - 80 LGs bought one new
                            81 LH
                            02 FXSTB Nighttrain
                            Jim

                            Comment


                            • #15
                              Part #28 disperses the oily crankcase ventilation fumes from the crankcase evenly into intakes for each cylinder.

                              You want it there for a permanent installation but if you took it out until you got a new airbox, it would probably be OK,... but there might be an oily mess inside the airbox.
                              -Mike
                              _________
                              '79 XS1100SF 20k miles
                              '80 XS1100SG 42k miles
                              '81 XS1100H Venturer 35k miles
                              '79 XS750SF 20k miles
                              '85 Honda V65 Magna ~7k miles
                              '84 Honda V65 Magna 48k miles (parts bike)
                              '86 Yamaha VMAX 7k miles

                              Previous: '68 Motoguzzi 600cc + '79 XS750SF 22k miles +'84 Honda V65

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