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Performance Problems GS550L

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    #1

    Performance Problems GS550L

    Hi All,

    I currently own a 1982 GS550L which has been problematic for a number of months now. Let me explain:
    Starting is ok, but after a while the idle is a bit lumpy. When I ride it on the road, the main problem occurs: - when I accelerate from stop up through the gears, I get to around 75-80 mph and I can?t accelerate any faster. At this speed the engine becomes very jumpy and sounds like it is misfiring slightly. If I release the throttle at all at this point, there is a flat spot and I am unable to accelerate again. In most cases I have to pull over to the side of the road and switch the bike off and on again. (It will die out anyway). Also, I fitted a pair of universal straight thru slash cut silencers last autumn which I think may have contributed to this problem. The problem was occurring before this time. It is really annoying and means that I can?t really ride over the speed of 65 mph before this problem kicks in! Another occurance of this problem is when climbing a long gradient over a mile or two. Even if I keep a constant 60 ? 65 mph, after a few minutes, the same old problem happens ? a flat spot and wanting to die out. Any ideas would be gratefully appreciated.

    Brendan
    Tags: None
    #2
    Re: Performance Problems GS550L

    I believe your problem is that you do not have a combustible mixture in the cylinders. Either there is not enough fuel, or there is too much air.
    At 75-80 mph, a 550 would be running completely on the main jets and those are not adjustable. The first thing I would do is verify fuel is available. Put the bike on the centerstand. Disconnect the fuel line from the petcock where it supplies the carbs. Put the end of the line in a quart container and turn the petcock to prime. Let it run until the quart container is filled. If there is consistant flow and the container fills, then
    there is no screen blockage to the petcock.

    Reconnect the fuel line to the carbs. Set the petcock lever to prime and wait 30 seconds. Return lever to run. Take a small container and drain a float bowl into it. This will be the full amount of fuel your float will allow. Mark that amount on the container. Take that container and a screwdriver with you. Take the bike for a run at 75 mph or so and when it starts to die out, turn the kill switch to off, pull in the clutch and coast to the side of the road. Drain the same float bowl into the cup. Check to see if there is the same level of fuel drained as before. The float bowl should always be full. If it is not, then you have a petcock diaphram problem and the petcock is not working correctly.

    If it is full, then it is an induction problem. Check that the carb mount tubes/rubbers are clamped tightly between the carb and engine and between the carb and airbox. Check the airbox for leaks. Do you have a filter in the airbox. No filter will lean the mixture. If you have installed pod filters, that will also have leaned the mixture. If everything is right and no air leaks are found, the airbox/filter is stock and the only modification you have made is to install shorty baffleless mufflers, my first approximation would be to increase the main jet size by two sizes. If you have added the mufflers and changed to pod filters at the same time, my best guess would be to increase main jet size by four sizes. What colors are you plugs showing on the center ceramic when the bike runs out of fuel?

    Earl
    Komorebi-The light filtering through the trees.

    I would rather sit on a pumpkin and have it all to myself than be crowded on a velvet cushion. H.D.T.

    Comment

      #3
      I just had my 81 gs550 cv carbs apart and found the screens under the float needle seats dirty. This kind of thing can cause the symptoms you describe.

      Comment

        #4
        Think Earl nailed it: fuel starvation. Caused by dirt or petcock vacuum probs.

        Comment

          #5
          Thanks

          Thanks for the info guys, must check out the items mentioned. I am a bit apprehensive when it comes to dismantling and servicing the carbs however!

          Comment

            #6
            Don't worry about your apprenhension on carb. work. The people here at this forum will get you through it. I don't know the link but there's one place on here that goes step by step on carb. work.

            Comment

              #7
              I think I found the link. Try this. http://www.thegsresources.com/gs_carbrebuild.htm

              Comment

                #8
                thanks

                Ok guys thanx for the advice! Got carbs off eventually on Monday night. In the process of taking them off one of the rubber feeder pipes from the carb to the cylinder head fell off. On closer inspection, someone had at a time, tried to use silicone or similar to reattach it to the metal flange which is screwed to the head. Methinks this is part if not all of the problem, as it was allowing air into the post-carb mix and making it much leaner. Possibly at speeds of 70-80 mph the extra air taken in would have created a mix so lean than it was incombustible! I have inspected the rest of the rubber pipes and they are in a similar condition. Are they a readily available part and if so who would deal in them and are they expensive? Anyway, with the carbs removed I will split them and service them. Any further ideas would be appreciated!

                Cheers,

                Brendan.

                Comment

                  #9
                  If you mean by saying "I'll split the carbs" that you are going to separate them from each other, I didn't do that because all that was needed was to make sure all the passages were clear and I did that by squirting carb cleaner spray through them all and then compressed air. The link I gave earlier about going through the carbs let me know what jets and needles and diaphragms to remove to get at the passages. If you're going to soak them in a bucket of carb cleaner then you need to make sure all the rubber parts are removed and that means separating them from one another to get at some of the "O" rings. Mine has pressed in plugs to drill out before you can remove the idle mixture screws and their "O"rings, springs and washers.
                  I'm thinking maybe since yours has run well recently that you could just replace the rubber boots that fell apart, the ones between the carbs and head and their "O" rings. Those "O" rings are the high heat type, teflon I think but wherever you get the boots should have the right "O" rings too. BikeBandit.com has lots of stuff. http://www.bikebandit.com/partsbandit/Default.asp try that.

                  While you've got the carbs off it would be a good idea to at least remove the float bowls to inspect and if you find it nasty in there you should probably clean them up. If you're carefull taking the float bowls off you may not need new gaskets for them.

                  Comment

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