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Engine bogging down while cruising

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    #1

    Engine bogging down while cruising

    Bike/engine are in signature.

    Sofar I've replaced the intake o-rings, replaced the airbox-to-carb boots, cleaned the carbs thoroughly, done a valve adjustment, got new spark plugs, and got a new petcock.

    I just now got in my first few days of real riding and it's a lot of fun. The only thing is, my bike has a major missfire/bogging down/flat spot problem. Here's the gist of it:

    At 50 KPH in third gear holding a steady cruise, I can feel the bike misfire now and then. When it does this, it slows down and then speeds up quickly. Very annoying.

    Then at 80 KPH at around 4500 RPM, the bike will bog down and slow down if I give it gas, but after a couple seconds it will pick the RPM's up, slowly. If I go full throttle it doesn't bog, but it doesn't accelerate as fast as it should.

    What's it sound like? Fuel delivery? Ignition? I checked the plugs and they looked perfect - no pitting or bright white or anything, just peachy. It feels like it's running out of gas. If I do a 0-100 KPH run, it'll do it just fine. Accelerating around town is fine. It's just higher speeds and cruising. It idles really well and with no load (IE neutral) it revs just fine.

    Fuel cap creating too much vacuum?
    Carbs plugged even though I cleaned them out twice?
    Ignition?
    Air leak? (doubtful, I don't see where it could leak from to cause a problem this dramatic)
    Tags: None
    #2
    Hi Mr. MrZig,

    Sometimes it's just a process of elimination. To your list I would add checking the float height. I've heard of these symptoms being caused by intermittent coils or igniter, or even bad valve timing. But I'm just guessing at some possibilities.


    Thank you for your indulgence,

    BassCliff

    Comment

      #3
      When I cleaned the carbs I adjusted the float height to spec..

      Here's what I did today:

      Cleaned petcock filter - it wasn't bad at all, although there was some rust at the bottom.
      Added a better ground from battery to R/R.
      Made fuel line more direct and more pointed down.
      Squeezed excess air oil out of air filter.

      And there was no change. Still bogs and missfires like crazy. I'm thinking the carb's might have gotten plugged again.
      I tested the spark of the plugs, and they came out light blue/violet.

      Also tested the resistance of the spark plug elbows and one came to 8.82k ohms, the other came to 9.62k ohms.
      The coils each read 3.9 ohms on primary. The secondaries with the caps attached are 21.2K ohms, and 22.1k ohms.
      I've also run it in prime with no change.

      Here's a couple pictures I took of the spark plugs:



      Last edited by Guest; 04-18-2009, 09:34 PM.

      Comment

        #4
        a couple of ideas...

        what were the carb diaphragms like?
        and, have you confirmed that you have the right size jets for your intake/exhaust setup?
        GS850GT

        Comment

          #5
          Originally posted by psyguy View Post
          what were the carb diaphragms like?
          and, have you confirmed that you have the right size jets for your intake/exhaust setup?
          Carb diaphrams were perfect.

          I havn't confirmed the jets, but I imagine they would be stock as everything else on the bike is stock.

          Comment

            #6
            Plugs look good. I'd have a look at the igniter.
            If you say you have rust in the tank that could be the issue also.
            1983 GS 1100E w/ 1230 kit, .340 lift Web Cams, Ape heavy duty valve springs, 83 1100 head with 1.5mm oversized SS intake valves, 1150 crank, Vance and Hines 1150 SuperHub, Star Racing high volume oil pump gears, 36mm carebs Dynojet stage 3 jet kit, Posplayr's SSPB, Progressive rear shocks and fork springs, Dyna 2000, Dynatek green coils and Vance & Hines 4-1 exhaust.
            1985 GS1150ES stock with 85 Red E bodywork.

            Comment

              #7
              Originally posted by chef1366 View Post
              Plugs look good. I'd have a look at the igniter.
              If you say you have rust in the tank that could be the issue also.
              If the igniter failed wouldnt it just shut the bike off?

              And yea the tank has some rust so im going to tear the carbs apart again..

              Comment

                #8
                Originally posted by MrZig View Post
                If the igniter failed wouldnt it just shut the bike off?

                And yea the tank has some rust so im going to tear the carbs apart again..
                No, the spark becomes irregular and causes situations like yours. I've seen it and chased the jetting issue to no avail.
                1983 GS 1100E w/ 1230 kit, .340 lift Web Cams, Ape heavy duty valve springs, 83 1100 head with 1.5mm oversized SS intake valves, 1150 crank, Vance and Hines 1150 SuperHub, Star Racing high volume oil pump gears, 36mm carebs Dynojet stage 3 jet kit, Posplayr's SSPB, Progressive rear shocks and fork springs, Dyna 2000, Dynatek green coils and Vance & Hines 4-1 exhaust.
                1985 GS1150ES stock with 85 Red E bodywork.

                Comment

                  #9
                  Originally posted by chef1366 View Post
                  No, the spark becomes irregular and causes situations like yours. I've seen it and chased the jetting issue to no avail.
                  How do I test it?

                  Comment

                    #10
                    The GS400 had points, not an ignitor. Of course, your bike has a different engine so not sure what's up with the ignition now. Sounds like time to pull off the ignition cover and have a look. If it has points, make sure everything is hunky dory in there.
                    Ed

                    To measure is to know.

                    Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

                    Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

                    Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

                    KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

                    Comment

                      #11
                      I'm guessing fuel delivery. You mention rust and that the problem seems more pronounced at a constant throttle position. Most flow/venting problems are more noticable at a constant throttle. I also think the plugs look on the lean side, though it depends on how long they've been in use. The ceramic insulator looks too white to me (keeping in mind plug pics are notorious for looking different in person).
                      All rust has to be removed and the cause fixed. Jets cleaned. Gas tank vent needs to be cleaned if any doubt. If you have floatbowl vent lines, are they clear and not pinched and breathing free to atmosphere?
                      I also wonder about the air filter. You say you squeezed excess oil out of it? An over-oiled filter should darken the plugs but I wonder what would happen if you ran without it just for testing purposes.
                      And on the seventh day,after resting from all that he had done,God went for a ride on his GS!
                      Upon seeing that it was good, he went out again on his ZX14! But just a little bit faster!

                      Comment

                        #12
                        The GSX400 in my GS400 has electronic ignition. Positive about that.

                        I think the rust isn't a big issue. What happend was I emptied the tank out, and washed it out with water. Flash rust occured, and I ended up swashing some phosphoric acid around in there. When I took the petcock out, there was only a little bit of rust on the very bottom. Not lots. Probably won't be an issue anymore.

                        Where is this mysterious gas tank vent? I don't have any other lines coming out of it except for the fuel/vacuum. Float bowl vent line is good.

                        I'm pretty sure it's a carburetor problem.. If it still persists after another cleaning then I don't know wtf.

                        Comment

                          #13
                          Bogging

                          I had a similar situation on my 80 GS1000E a slight hesitation like I had backed off the throttle just a bit. It would pick back up but it was disconcerting at best. My problem was a terminal?! terminal on the connector going to the fuse box. Unplugged it and replaced the offending parts crimped and soldered them and all is well now, hope that is some help.
                          1980 GS1000E

                          Comment

                            #14
                            Originally posted by mustangflyr View Post
                            I had a similar situation on my 80 GS1000E a slight hesitation like I had backed off the throttle just a bit. It would pick back up but it was disconcerting at best. My problem was a terminal?! terminal on the connector going to the fuse box. Unplugged it and replaced the offending parts crimped and soldered them and all is well now, hope that is some help.
                            hmmm interesting. You might've had an ignition cut out by the wiring. I'm not so sure that's what my problem is, but you never know. I don't have a fuse box but I do have a lot of old connectors

                            Comment

                              #15
                              I ripped the carbs apart and they looked pretty good. The main jet and needle jet, and the jet needle, all look perfectly fine. I havn't taken the pilot jets out yet. They're a pain.

                              The float heights are as follows:

                              Left side carb: 23mm
                              Right side carb: 22mm


                              Clymer says for all models except the GS450, it should be between 25.6mm and 27.6mm. The GS450 should have between 21.4mm and 23.4mm.

                              I'm basing it off the GS450 model, as I think they're the same carbs as mine, and by doing so, my float level is correct.

                              I'm kind of at a loss..
                              Last edited by Guest; 04-19-2009, 07:29 PM.

                              Comment

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