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81 GS650g intermittent bogging

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    81 GS650g intermittent bogging

    hey there,

    im looking for some opinions on my bike.

    recently (last 50 miles ish) the bike seems to be starving of fuel. but only intermittently. typically goes like this,

    start bike, starts right up with a small bit of choke and then as soon as it starts to come up a bit in rpms i lower choke and let it warm up just a little.

    start off down the backroad i live on and when i hit the straight i start to lay into it from a stop, 1st 2nd are fine typically and pull and i feel no hesitation.
    3rd is usually where i start to feel some hesitation as if it's running ok (no sputtering or anything) but down on power and it kicks in with dropping cylinders it almost feels like as the motor starts to make instead of it's inline 4 rev'sness more of a "bog bog bog bog" sound as if it's not firing or maybe flooding out? it does this all the way up to 5th and more so in 5th under load it would seem.
    it doesnt die out and im fairly sure it's not running lean. if i let off gas and coast for a bit i can pick it back up and it will pull then hesitate and sometimes it just straight pulls all the way through with no problems.

    now, in the last 50 miles the only work ive done was new clutch springs and oil, and i reseated the exhaust (if anything this would have changed AFM) as in the PO stripped out bolts so the exhaust hadnt been seated to the block of the bike so i put studs in and it's now flush so instead of only putting 60% of exhaust through the tubes it's hopefully putting 100% (ran fine initally after doing exhaust for like 10 miles) i speculate that PO ****ed with carbs to make it run ok like that, so when i took them apart i put back to stock settings where available. (all jets were stock and needles when i opened them)


    list of things checked and results
    plug chop reveals im running just a smidge rich if anything, really want to do another one and cut engine while it's bogging to see if that shows anything more
    fuel delivery to carbs is good as that is 1st thing i replaced was a solid line direct to carbs as the tank has a finer mesh then any filters i was using.
    took carbs out (5 times) adjusted floats and did a "cleaning" (1 full can of carb cleaner in a rubber maid and blasting every part i could and through every hole to remove dirt with them taken apart but not seperated)
    everything was stock settings (stock bike also with stock foam filter and exhaust)
    petcock is totally cleaned and reassembled and runs same on prime as on vacuum side.
    took side cover off and stator has the spring it's supposed to (not sure on that was just told to check but i have no idea if i did it right)


    things i want to test when i head back to where the bikes at.

    open float bowls and put petcock on prime and see the constant flow into the carbs to see if it's just not flowing into the bowls right.
    swap ignition coils (they both tested out to 4.6 ohms which appearently is within range?) to see if it switches sides
    starter fluid mist around the airbox for leaks.
    run with no tank top to eliminate a vacuum lock.

    any other ideas, tests i could do please let me know.

    #2
    So this happenned recently- does this mean it was running ok? Or are you still in the "gettinginbackonroad" stage?

    and what dies this mean......
    "Took side cover off and stator has the spring it's supposed to (not sure on that was just told to check but i have no idea if i did it right"

    are you refering to mechanical advance gizmo behing little round cover?
    1981 gs650L

    "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

    Comment


      #3
      EZ is to see by turning to prime when it happens...

      I still have one bike that occasionally tends to run a bit odd after a steady constant run and switching to prime OR opening the throttle while riding makes it flow properly again...but it usually happens slowing /coasting to a lower speed limit so goosing the throttle is not a good idea . It will go away once on the highway again.

      petcock is totally cleaned and reassembled and runs same on prime as on vacuum side.
      I too did this but without any useful result...the way these work in reality, in my imagination, is as a kind of vibration to meter fuel according to vacuum ...on a steady run they don't move much...a vibration more like..

      In my case Changing the petcock diaphragms tiny oring helped a lot- a least now it doesn't cough and jerk as it did in the early instances....polishing away at the actual valve is maybe where the exact problem lies but tricky...not meant to be "fixed" ...

      if you're less lucky, well, I expect you'll turn over all sorts of nasty rocks
      Last edited by Gorminrider; 04-30-2017, 11:16 AM.

      Comment


        #4
        I probably should have asked OP if he still had stock airbox or made the podleap.

        As to petcock.. why bother mucking with them - there's plenty of other fun stuff to do

        1981 gs650L

        "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

        Comment


          #5
          @tom

          yes... lol to both that is, it was on road last season and had issues when i pulled it out of storage.

          also yes, the ignition advance behind the side cover.

          also ALL stock, airbox, even foam filter.

          @gorminrider

          would do it on all petcock settings with or without vacuum components being installed in the petcock housing. and with a seperate test tank.


          BUT...

          i got it working. not sure exactly what it was, but i took carbs out all the way and soaked them and when i put them back in it seems to have cleared up. my speculation was that a jet wasnt all the way cleared out.

          the bike pulls now all the way up.

          though i will say after going for a couple mile ride my idle started to be off. seems like it would go low and catch up so i may have to resynch again.


          anybody know of a guide to proper resynching?

          i have a similar gauge to this.



          its really just about what cylinder is supposed to be where as my clymer uses the suzuki mercury style gauges and isnt super informative about what cylinder should read what just that it looks like 2 outer cylinders have more vacuum then the 2 centers?

          Comment


            #6
            It's a miracle! Yes, some orifice probably got cleaned out, or maybe carbs got tired of you yanking on them.. Have you bench sync them? This would get you real close and then you finetune them with your dial gizmos. Someone familiar with your sync tool should show up here, but did you follow Basscliff's explanation with his colortune setup?

            1981 gs650L

            "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

            Comment


              #7
              @tom

              no it was more, look at the clymer manual. and it has a gauge pictured similar in style to that one, same as this

              Motion Pro SyncPro Carb Tuner Synchronizer Tool with 5mm adapters. SyncPro Carb Tuner. SyncPro Instructions PDF File. Includes hoses, 5mm adapters, in-line restrictors and instructions. 5mm adapters are used on many Honda and Suzuki models.


              and use that as a seat of the pants reference (as it didnt give any units of vacuum such as -Hg to go by, only that it seemed to have 2 outer cylinders have more then 2 inner)

              so using my style gauge i just put the outer cylinders 2 lines more vac then the inner (NASA is totally jealous of my accuracy for sure.....)

              Comment

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