Announcement

Collapse
No announcement yet.

Nearly at my wits end with this bike. Idle takes off like a rocket with the tank on.

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Nearly at my wits end with this bike. Idle takes off like a rocket with the tank on.

    Hey All,

    I was really hoping I'd be putting the seat and side covers on this thing and taking it for a safety soon but unfortunately another gremlin as popped up that is beyond my limited knowledge and I haven't found a solution to point me in the right direction using the search.

    Cleaned the carbs (Ultrasonic, carb cleaner, set floats), new o-rings, new carb boots, airbox boots, filter (an OEM style foam one), petcock rebuild, all new electrics including a SSPB. I got the carbs synced up and the bike seemed to be running pretty well. Throttle response was decent and it held idle where I set it. I put the tank on, connected the vacuum tube, made sure I was flowing fuel by installing a temporary run of clear tubing. All seemed well, but with the tank on, it would struggle to start, wouldn't hold idle and the RPMs would take off suddenly.

    So I took the tank off thinking I must have disturbed something while installing it. Resynced the carbs, double checked for air leaks and that was all good, put the tank on again and had the same issue. If I get the bike running without choke and set the idle to 1000 or so RPM, if I blip the throttle one of two things happen. Either the bike bogs and nearly dies, or the revs take off upwards of 4000. I dial back the throttle adjuster to get the RPM to fall back down and then the idle goes through the floor and it either lumps around at 500-600 and dies, or just dies right away. The adjuster is coming to rest on the lower stop when fully turned out, the throttle linkage is free and has a slight bit of slack before it picks up. I'm really at a loss for what to do next. I had set the timing for the Dyna-S way back so I hooked a timing light up in hopes I could dynamically tune it, but since it won't hold a consistent idle with the tank on it's a lost cause.

    Where do I go next?

    #2
    Are your throttle cables run correctly? Do you have one or two? Could you post some photos?
    :cool:GSRick
    No God, no peace. Know God, know peace.

    Eric Bang RIP 9/5/2018
    Have some bikes ready for us when we meet up.

    Comment


      #3
      photo 1.jpgAs you can see, the cable has a bit of slack, when I twist the handle it quickly goes away. Throttle response was smooth and behaved as expected with the tank off. When it's released it snaps back right to the original position every time. There's nothing that seems to be hanging it up. When I turn the knob to adjust the resting position the RPMs increase or decrease as expected. With the tank on the bike can idle really low and then suddenly climb to redline without any throttle input, and when the throttle is turned the bike either bogs and stalls or the revs climb abnormally high and then hang long after the throttle has returned to the resting position. The only way to get them to come back down is by turning the idle screw till the butterflies close entirely.

      Comment


        #4
        photo 2.jpgI also pulled all 4 plugs and they all look like this. They aren't very old (just had the sync and tinkering time on them. Maybe an hour tops). I could put brand new ones in I suppose but that doesn't explain why things seemed to work much better when the tank was off. Good news is it doesn't seem to be running lean.

        Comment


          #5
          Intermittently functioning petcock. Hmmm... That's a possibility.
          Try running it with the gas caps off first. See if that helps. It could be struggling to draw fuel from a vent clog. (Not likely but possible)
          If it's not that, the petcock is wonky and operating sporadically or you have a partially collapsed fuel line.
          Just a few weirdo possibilities to help troubleshoot.

          Comment


            #6
            What I'm wondering is where the cables are routed. Is the tank pushing one of them down? Did you run new cables or are they the same ones as before? If new, did you route them exactly the same way? If you don't have a manual, here is the one from Bikecliffs webpage. On page 684 shows the proper routing of you throttle cables.
            :cool:GSRick
            No God, no peace. Know God, know peace.

            Eric Bang RIP 9/5/2018
            Have some bikes ready for us when we meet up.

            Comment


              #7
              Originally posted by loud et View Post
              Intermittently functioning petcock. Hmmm... That's a possibility.
              Try running it with the gas caps off first. See if that helps. It could be struggling to draw fuel from a vent clog. (Not likely but possible)
              .
              Thats where I would go first.

              Comment


                #8
                How much fuel is in the tank, and when the tank was off, were you running the bike off an auxiliary fuel source, or the tank in a higher position than where it would sit on the frame?
                '83 GS650G
                '83 GS550es (didn't like the colours in the 80's, but they've grown on me)

                Comment


                  #9
                  Originally posted by Runeight View Post
                  Thats where I would go first.
                  Although a vent issue would either work or not work I would think. Been thinking on this myself.

                  Comment


                    #10
                    Originally posted by loud et View Post
                    Intermittently functioning petcock. Hmmm... That's a possibility.
                    Try running it with the gas caps off first. See if that helps. It could be struggling to draw fuel from a vent clog. (Not likely but possible)
                    If it's not that, the petcock is wonky and operating sporadically or you have a partially collapsed fuel line.
                    Just a few weirdo possibilities to help troubleshoot.
                    I could see the bog coming from a bent or collapsing line or a weak feed from the petcock, but how would that make the rpms sky rocket? I've seen this with a cable that was routed in the fork wrong, where it would get pulled in a turn and make the rpm shoot up. The cable routing in the manual shows the cable should go over the right tank perch, but without seeing how it is routed in reality, it's still a guess. Also did you change the handlebars?
                    :cool:GSRick
                    No God, no peace. Know God, know peace.

                    Eric Bang RIP 9/5/2018
                    Have some bikes ready for us when we meet up.

                    Comment


                      #11
                      Starting to sound like compound problems. Try running it off a remote tank again. If it runs well like that then put the tank back on but keep running off the remote tank. That should eliminate any kind of mechanical issue with the tank or cable. I've you have her running nicely on the remote tank with the real tank mounted then you should hook the tank back up and see if it is a fuel problem.

                      Comment


                        #12
                        Sounds like a faulty petcock to me
                        1984 GS1100GK newest addition to the heard
                        80 GS 1000gt- most favorite ride love this bike
                        1978 GS1000E- Known as "RoadKill" , Finished :D
                        83 gs750ed- first new purchase
                        85 EX500- vintage track weapon
                        1958Ducati 98 Tourismo
                        “Remember When in doubt use full throttle, It may not improve the situation ,but it will end the suspense ,
                        If it isn't going to make it faster or safer it isn't worth doing

                        Comment


                          #13
                          Originally posted by gsrick View Post
                          I could see the bog coming from a bent or collapsing line or a weak feed from the petcock, but how would that make the rpms sky rocket? I've seen this with a cable that was routed in the fork wrong, where it would get pulled in a turn and make the rpm shoot up. The cable routing in the manual shows the cable should go over the right tank perch, but without seeing how it is routed in reality, it's still a guess. Also did you change the handlebars?
                          I was thinking if he has a low or struggling idle issue due to poor fuel flow from the petcock or a bent fuel line and he adjusts the idle up. .....then the petcock starts flowing better or the fuel line relaxes and either one starts filling the bowls then the increased fuel supply would make it run properly but having adjusted the idle up......it would seem like it's racing.
                          Basically like he is messing with the master idle and sporadic fuel flow making the situation hard to pin down what's happening.
                          Something like that. Lol

                          Comment


                            #14
                            I looked at your first picture, tighten the bottom nut on the throttle cable adjuster, it's loose. I bet your problem will go away.

                            V
                            Gustov
                            80 GS 1100 LT, 83 1100 G "Scruffy"
                            81 GS 1000 G
                            79 GS 850 G
                            81 GS 850 L
                            83 GS 550 ES, 85 GS 550 ES
                            80 GS 550 L
                            86 450 Rebel, 70CL 70, Yamaha TTR125
                            2002 Honda 919
                            2004 Ural Gear up

                            Comment


                              #15
                              Originally posted by cp___32 View Post
                              [ATTACH=CONFIG]45744[/ATTACH]As you can see, the cable has a bit of slack, ...
                              What I see in that picture is a cable assembly that is not held tightly to the bracket. Note the angle between the cable and the bracket. Tighten one of the nuts to fix that. Can't say whether to tighten the upper one or the lower one, it depends on which one leaves the proper amount of slack.



                              Originally posted by gustovh View Post
                              I looked at your first picture, tighten the bottom nut on the throttle cable adjuster, it's loose. I bet your problem will go away.
                              you noticed that, too.

                              .
                              sigpic
                              mine: 2000 Honda GoldWing GL1500SE and 1980 GS850G'K' "Junior"
                              hers: 1982 GS850GL - "Angel" and 1969 Suzuki T250 Scrambler
                              #1 son: 1986 Yamaha Venture Royale 1300 and 1982 GS650GL "Rat Bagger"
                              #2 son: 1980 GS1000G
                              Family Portrait
                              Siblings and Spouses
                              Mom's first ride
                              Want a copy of my valve adjust spreadsheet for your 2-valve per cylinder engine? Send me an e-mail request (not a PM)
                              (Click on my username in the upper-left corner for e-mail info.)

                              Comment

                              Working...
                              X