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Dead cylinder #4!

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    #1

    Dead cylinder #4!

    Hi everybody. I was hoping to get some opinions on how to troubleshoot a dead #4 cylinder. I recently got a GS550T, 1981. First thing I did was clean the carbs, replace the boots and o-rings, and make sure there weren't any air leaks. I rode the bike a few days, thinking it was all good until I checked the plugs. Cylinders 1,2,3 were whitish, and 4 was brown. Thinking I didn't have my mix screws right, I adjusted them.

    After riding the day after, I noticed that cylinder #4's exhaust was pretty cool. I replaced plug #4 with a new one and made sure it was firing by taking off the coil and plug and grounding the plug on the engine, watching for spark. There was a thick blue spark. I readjusted the mix screws, but it seemed that cyl 4's screw wasn't doing anything. Felt the pipe, still cold. Then I tried to pull cylinder 4's boot while the bike was firing to see if the RPMs would drop, got a big shock, but no change.

    When I pulled the plug, it wasn't wet at all so it seems that that cylinder may not have been getting any fuel. However, the first plug I had in there fouled and turned black after running for a day, so there must have been fuel flow at one point... The original plug was from the PO, but was white and was firing I looked when I bought the bike)

    I haven't adjusted the valves, but I have checked them. There were a few that were tight at .03mm, but still in spec. I plan on adjusting them this weekend, but I want to solve this dead cylinder issue first....

    What do you guys think as for next steps in troubleshooting? I was thinking of cracking #4's carb bowl drain plug to see if theres fuel in there and perhaps checking for a sticky float valve.... Don't want to pull the carbs again and clean then, as I did a good job and followed Cliff's guide.

    Hmmm....oh and, I checked compression... it was good- around 140 if I recall correctly.

    Thanks,

    Nick
    Last edited by Guest; 04-01-2011, 07:39 PM. Reason: adding a bit of info on compression
    Tags: dead cylinder, not firing on all four
    #2
    Originally posted by ligamentx View Post

    Don't want to pull the carbs again and clean then
    Nick
    I can't blame you, but...

    That sounds like where the body is buried.
    sigpic Too old, too many bikes, too many cars, too many things

    Comment

      #3
      Hehheeheh
      got a shock you say
      leaking hi tension lead arcing to the engine block and not firing the plug sufficiently or intermittently resulting in a sooted up plug.

      Swap you plug caps from a good working cyl to the #4

      Comment

        #4
        I'm going to try to pull the #4 bowl and check for fuel... do float valves all of a sudden get sticky? I also forgot to mention I dropped the bike on my first ride doing some slow speed manuvering :\. Embarassung, but it has been a whole winter since Ive ridden! It died while tipped over but started back up with 10-20 second of intermittent cranking after the fall- maybe I could have fouled the plug on that first ride and then gotten the float valve stuck? I'm hoping it's that easy...

        Comment

          #5
          Loosen the drain plug to see if fuel is in the bowl to eliminate a stuck closed float valve.

          edit: I see we had the same idea at the same time.
          1982 GS1100GL Citrus County, FL

          a rare outsider and was only built until 1983. Who still has one, it gives her so little.

          Comment

            #6
            Originally posted by JEEPRUSTY View Post
            Hehheeheh
            got a shock you say
            leaking hi tension lead arcing to the engine block and not firing the plug sufficiently or intermittently resulting in a sooted up plug.

            Swap you plug caps from a good working cyl to the #4
            Thanks, I'll try this tomorrow- is this repairable or would It require a new boot/coil?

            Thanks for the help... would this result in a dry plug? Or maybe idling the bike for a while didn't get enough fuel in the cylinder to have a wet enough plug to notice...

            Nick

            Comment

              #7
              Originally posted by ligamentx View Post
              Thanks, I'll try this tomorrow- is this repairable or would It require a new boot/coil?

              Thanks for the help... would this result in a dry plug? Or maybe idling the bike for a while didn't get enough fuel in the cylinder to have a wet enough plug to notice...

              Nick

              Caps go bad NGK makes cheap HQ replacements.
              You will have to refer to NGKs partsfinder page for the correct resistance cap etc.

              I have had insane probs cured by caps.

              Comment

                #8
                So was all this carb cleaning done last year?
                sigpic Too old, too many bikes, too many cars, too many things

                Comment

                  #9
                  No, I just purchased this bike non-running this year... got it to this point. I had a little honda rebel that I sold last year... big difference :P

                  Comment

                    #10
                    You might want to clean those carbs thoroughly again.
                    Cowboy Up or Quit. - Run Free Lou and Rest in Peace

                    1981 GS550T - My First
                    1981 GS550L - My Eldest Daughter's - Now Sold
                    2007 GSF1250SA Bandit - My touring bike

                    Sit tall in the saddle Hold your head up high
                    Keep your eyes fixed where the trail meets the sky and live like you ain't afraid to die
                    and don't be scared, just enjoy your ride - Chris Ledoux, "The Ride"

                    Comment

                      #11
                      The CV carbs can not be too clean. The #4 carb still has a problem

                      Comment

                        #12
                        Originally posted by ligamentx View Post
                        I replaced plug #4 with a new one and made sure it was firing by taking off the coil and plug and grounding the plug on the engine, watching for spark. There was a thick blue spark.
                        Hmmm....oh and, I checked compression... it was good- around 140 if I recall correctly.
                        Compression, spark and valve clearance isn't your problem.

                        did you bench sync the carbs when you reassembled them? have you vacuum sync'ed them yet?
                        De-stinking Penelope http://thegsresources.com/_forum/sho...d.php?t=179245

                        http://www.thegsresources.com/_forum...35#post1625535

                        Comment

                          #13
                          I haven't done any itype pf synching. I have a vacuum guage... Would this help a lot?

                          Comment

                            #14
                            In spite of the disparate claims made so far my plug cap check is free and prevents a lot of other very hard work if correct.

                            Comment

                              #15
                              Just traded 1 and four plug caps, then the plugs. No change, 4 is still dead

                              Comment

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