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  • Rear Cylinder Issues

    Hi All;
    Some of you might have seen my post and trouble shooting comments on Facebook about this issue but now that I've run through as far as my friends and I can go with it I thought I would post here and see what else I can do. Here is what happened and whats been done.

    The bike had been running hotter to the feel than it used to and was running a little rough. One day down freeway had a big backfire and loss of power. As I went to side of the freeway the power came back for about 2 seconds then went away again and this continued till I got her to a stop. Got her home and listened and only the front cylinder was running. Looked at carb and the diaphragm cover was blown out with the spring hanging out. I replaced the cover as diaphragm looked fine and no change.

    Changed plugs and there was no change. Checked compression and that was fine. Checked spark using spark testing tool and at first no change, however as we moved the wire around we got spark and cylinder ran if we held in right position. Decided coil and wires were bad. Got new coil. Installed coil and had small change. While running the front cylinder ran fine and rear would come on for a second and then stop, then come on for a second and then stop. Thought resister caps were bad. Got new resister caps and testing resistance with fluke tester. Neither old or new caps cave any reading (however this could be me not knowing how to use a tester right). I installed new caps and same thing happening.

    So now I'm not sure where to look. With those new components and having compression and cylinder working at times, what could be the issue I'm having?

    Thanks for the guidance on this as I really can't afford to take her in anywhere.
    Remember. No matter where you go, there you are.

  • #2
    What year? Not all are created the same. Sounds like possibly sticky valve syndrome.

    Comment


    • fastjohnny
      fastjohnny commented
      Editing a comment
      I agree that SVS is a problem that no spark in the rear cylinder could be the result of. Mine is an 05 as well. I ditched the resistors in the caps and replaced them with a piece of heavy (4 or 6 AWG if I remember correctly) solid wire. A lot of us did that back in the days of the old forum....resistors in the caps are not needed....just another thing to f*%& up. I don't know how to access the old forum, however.

  • #3
    2005 midnight silverado.
    Remember. No matter where you go, there you are.

    Comment


    • #4
      Not sure I can help much, but hope to offer some support. You've done a compression test and that looks good. So from my limited experience, that's a good start. It takes fuel, compression, and spark to run. On a single carb'd engine I'd presume fuel is there since the front cylinder seems to run good. But that wouldn't rule out a vacuum leak on the rear cylinder, especially if you had a serious backfire.

      If you're not getting consistent spark on the rear cylinder I'd start my focus there. Maybe use your testing method on the front to see if you're getting consistent spark there. That might help identify if your testing method is suspect.

      Comment


      • #5
        If wiggling the wire fixed it you are gonna have to keep wiggling wires until you figure out what wire has the bad connection. I had the exact thing on my Lawn tractor and found a 1/2 broken thru wire that when it got hot or vibrated in a certain way the cylinder would cut out. It took a few times of messing with it to find the wire that was broken because when I wiggled it and it fixed it I couldn't always wiggle it to cut out again to narrow it down to the correct wire.

        Comment


        • #6
          Make sure the throttle cables are not arcing to ground the positive lead on the coil . The throttle cable has a metal housing and it slides back and forth past the positive lead for the coil. I just wrap mine

          Comment


          • #7
            Does it make a difference which one of the plug wires you "wiggle" to get spark, or are they both (for the rear cylinder) not working all the time? You're gonna have to figure out where the fault is in whichever wire is suspected as being bad. I imagine once you've found the problem and fix it you will then be suffering from SVS which is pretty easy to fix.

            Comment


            • Bikerron
              Bikerron commented
              Editing a comment
              “... once you've found the problem and fix it you will then be suffering from SVS which is pretty easy to fix.”

              Never read about any of the ‘05s suffering from SVS.

            • fastjohnny
              fastjohnny commented
              Editing a comment
              SVS was a problem in most 04's and '05's

          • #8
            Not most 04 and 05's, mostly in those 2 years. I have 3 w no problems baby. He could have fried coil syndrome, must use VOM to test as it will appear spark correctly.
            .

            Comment


            • #9
              Well I gave up and got her to a mechanic yesterday. Just out of the scope of my ability as someone who has never before worked on much as far as vehicles. So here's to crossing fingers on the cost. lol
              Remember. No matter where you go, there you are.

              Comment


              • #10
                UPDATE; 2 hours in the shop it was found to be the wire near the fuse box that feeds the rear ignition coil had worn. Tech said just about worn in two. That's why intermittent spark and firing. Glad it was something simple.

                She does have a little backfire when letting off throttle and slowing down which is new. Going to run a good dose of sea foam through her and see what happen.
                Remember. No matter where you go, there you are.

                Comment


                • davej
                  davej commented
                  Editing a comment
                  That is the same exact problem I was talking about above that happened with my tractor. Mine was also the coil feed wire. lol

              • #11
                How did it wear down typically they wear down where the throttle cables Pass by the coils under the gas tank on right now outside

                Comment


                • #12
                  IM THINKING ITS the wire from the fuse box to the ign coil

                  Comment


                  • #13
                    According to tech and the repair invoice it said the wire coming from the ECM. I didn't know a carbed engine had an ECM but what do I know. (very little in case you are wondering). He showed me it was behind the fuse box coming off a connector that lead to the ignition coil.

                    I also didn't know they rejetted my carb etc. He went there first. I asked if it was jetted to aftermarket intake and exhaust and they said yes. However I noticed that my choke acts differently now. When I pull it all the way out it revs the engine higher like I would think a normal choke would do. (mine didn't do that before) but now when I push it all the way in its starving for fuel and idles poorly. If I pull the choke out ever so slightly I can have it idle like it used to and stronger. Not sure what jet and float needle he used and adjusted to though.

                    The link should take you to the picture of what he did on the service invoice.

                    https://photos.app.goo.gl/TMGgzkNTqtBreiJw8
                    Remember. No matter where you go, there you are.

                    Comment


                    • #14
                      I would ask what jets they installed vs what jets were in it before. I would also make them fix whatever they fucked up to make it continue to run shitty, it may be as easy as an idle or pms adjustment. I will also guarantee that they didn't install the 172.5 main and 40 Mikuni pilot jet that has been proven to be correct. If they changed the needle I would want to know why. If it already had an adjustable needle in it there was no reason for change except to charge for parts and I would want the old adjustable needle back. It sounds like the guy did good finding the broken wire but not on the carb. IMO for the problem you had the Carb should have never been suspect being a single carb feeding both cylinders. A carb problem would have affected both cylinders and would not have any effect one spark.

                      Comment

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