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1978 Gs550 bogging down

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    #1

    1978 Gs550 bogging down

    This is gonna be a big dumb post that has me incredibly confused, so i'm going to apologize now if i look like an idiot. Or if the things i'm thinking are off the wall hah.

    My bike totally stock except for a mac 4 into 1 exhaust. I ran last year and this year with no problems. It ran great, and sounded great. I rode everywhere and everything was fine.

    So like 2 days ago it started running a little funky. It would be fine off the line, and then around like 4k rpm and up it gets boggy. Not like awful, the bike won't run boggy, but to where going up a hill speed drops like crazy. And i can't downshift because it bogs there still. I don't really know how to describe it, other than it feels like it's "4 stroking". I know it's not. I'm dumb but i'm not that dumb. After having my 2 stroke bike 4 stroke all the time, that's the closest thing i can describe it to.

    All my carb boots are in order and tight, no leaks. I took my exhaust apart because my dad said i could have a clog. No clog. I took my petcock off thinking maybe it was a little dirty and at high rpms couldn't get enough gas to fill the bowls. Nope. It's clear and clean. I checked my air filter and it's solid, could probably get a new one, but it certainly isn't ruined or unusable. I changed all my spark plugs and gaped them correctly.

    So i don't think it's my jetting, based on the fact that it rode fine all last year with no problem. It ran fine and the pipes aren't turning blue or anything to show me something is wrong.

    I am due for a valve check, and i know i have 2 loose valves. Is it possible that they are kind of "floating" at high rpms and causing this problem? Because that's where i'm thinking my problem is. But i don't really know if that's possible. It just makes sense to me.

    Any thoughts would be appreciated, for i am confused and lost. If you need more information i'll provide what i know.

    Thanks for reading.
    Tags: None
    #2
    Maybe the carbs got mussed up over the winter, happened to me on a freshly rebuilt set that I did not properly treat the gas or drain the bowls.

    Your in a good place to have issues...many members in the area who can likely help if needed

    Comment

      #3
      It's not valve float unless you're above about 10,000 RPM. Some of your valves may be too tight. Adjust them all, it's very important that none get too tight. Carburetors could be clogged somewhere. Could be a load of bad gas. Could be a lot of things. Fuel tank vent, kink or split in a vacuum line, blocked fuel filter, a lot of things. It could even be an ignition thing, are your points functioning normally, timing spot on, good strong sparks, good tight wires?
      http://img.photobucket.com/albums/v5...tatesMap-1.jpg

      Life is too short to ride an L.

      Comment

        #4
        My vacuum lines are good and solid, my points are clean and gaped correctly as well. I guess it could be a gummy carb, but the bike didn't sit for more than like 1 week this winter. I made sure to ride it and keep clean gas in it.

        Comment

          #5
          I shot Steve a text, so i'm hoping he'll have something insightful for me. He normally does haha

          Comment

            #6
            Originally posted by DamKevinBoyd View Post
            My vacuum lines are good and solid, my points are clean and gaped correctly as well. I guess it could be a gummy carb, but the bike didn't sit for more than like 1 week this winter. I made sure to ride it and keep clean gas in it.
            That eliminates a lot, when were the valves last adjusted?

            How is the compression?
            http://img.photobucket.com/albums/v5...tatesMap-1.jpg

            Life is too short to ride an L.

            Comment

              #7
              I had a similar issue last year with my 550 and turned out to be small leak in the vac line that turn the petcock on. It was on the carb side of the line and right where it slid onto the carb. Snipped an inch off the end and rehooked it up and havent had an issue since.

              I would be going down the freeway and I would just start losing power like I was running out of gas. If I pulled over for a minute it would be fine then for while. Figured it was refilling the bowls on the carbs once I pulled over and wasnt using as much gas as flying down the freeway.

              Hope you get it fixed soon and back to riding!

              Comment

                #8
                Originally posted by tkent02 View Post
                That eliminates a lot, when were the valves last adjusted?

                How is the compression?

                Valves were last adjusted at 18,600 miles, i'm at 21,100 now.

                I'm not sure on my compression, i've got a gauge and can check that out tomorrow.

                Comment

                  #9
                  2,500 miles ago, and none were too tight then?

                  As a test, plug the vacuum line and run it on PRI to see if it gets better. Don't leave it there!

                  Does it run the same on a full tank of gas as it does near empty? Tried cracking the gas cap to see if it's a tank vent thing?
                  http://img.photobucket.com/albums/v5...tatesMap-1.jpg

                  Life is too short to ride an L.

                  Comment

                    #10
                    Nope, none were tight. All but two were perfect, two were just barely loose and are getting changed when i do them.

                    I'll try that tomorrow too.

                    I haven't noticed any difference in full/empty tank performance. I've filled up and ran the tank to reserve in one ride a few times and haven't noticed anything

                    Sorry if it sounds like I'm shooting down everything, I'm not trying to hah. I appreciate the help

                    Comment

                      #11
                      A couple valves a little loose won't have any effect on anything. Try the tank vent, look again for a split in the vacuum line, it has to be something simple. Are you running an inline fuel filter? If you are sometimes they can effect fuel flow. If you are not a particle of something could be blocking some passage in a carburetor.
                      I found a small chunk of wood the size of a toothpick tip partially blocking a fuel inlet needle valve once, on a carb with the screen on the needle valve and with the petcock screen in place. Dunno where it came from but it ran like crap especially at higher power..
                      http://img.photobucket.com/albums/v5...tatesMap-1.jpg

                      Life is too short to ride an L.

                      Comment

                        #12
                        Make sure advance is moving freely -
                        1981 gs650L

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

                        Comment

                          #13
                          UPDATE!!!!!!

                          I just checked my coils, got underneath and looked and the left side coil when sitting on the bike is leaking oil. It also tested bad. So i'd say it's safe to blame that.


                          Any links to some good ones? I did a quick search and found mostly after market ones, but found original ones on bike bandit for 122 each (ouch)

                          Here's a quick pic of the leak, or what i can see of it. It's for sure coil oil, it's thick like molasses. http://i.imgur.com/kERBhCN.jpg
                          Last edited by Guest; 04-16-2014, 06:29 PM.

                          Comment

                            #14
                            Originally posted by DamKevinBoyd View Post
                            UPDATE!!!!!!

                            I just checked my coils, got underneath and looked and the left side coil when sitting on the bike is leaking oil. It also tested bad. So i'd say it's safe to blame that.


                            Any links to some good ones? I did a quick search and found mostly after market ones, but found original ones on bike bandit for 122 each (ouch)

                            Here's a quick pic of the leak, or what i can see of it. It's for sure coil oil, it's thick like molasses. http://i.imgur.com/kERBhCN.jpg
                            I think I have one, will have to check

                            Comment

                              #15
                              Originally posted by nejeff View Post
                              I think I have one, will have to check
                              that would be cool if it's in good usable shape haha. pm me if you want when/if you find it! i appreciate the help

                              Comment

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