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Help !!!!!!!!!!!!!!!!!!!!!!!!!!!!

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  • #1

    Help !!!!!!!!!!!!!!!!!!!!!!!!!!!!

    My bike is running like crap. Let me tell you whats going on. Cranks up great, runs great, well for the first 10 or 15 miles it does. Then it starts to miss like it's running on 2 or 3 cylinders. It never does it till I get on the interstate. I can run all over town for hours and it never does it, let me get on the interstate and run at a steady speed 65-75 mph for 20 mins or so and then pull off the interstate at an exit ramp, come to a stop at the stop sign and when I start to go again it acts like I'am running on 2 or 3 cylinders. It also will backfire if I try to force it to go faster but if I back off the throttle a little and don't force it, it starts to smooth out and pick up the other cylinder. Does this sound like it's electrical or carbs or what. I sure could use some help with this guys, I'am lost on this one. Not sure where to start.
    Chris 79 XS11F With mods....!!!!!! 2005 FXST Harley Softail
    Tags: None
  • #2
    Check pickup coil wires very carefully. may also have coil going bad. my bike did something similar only happened on interstate. finally found out it had a bad coil . you could check coils cold ride bike then check hot to see if coil is bad .don't have book in front of me for specs. would think fuel problem would be present all the time. hope this helps.
    when you want something bad enough, don't let anything stand in your way, and don't take "no" for an answer. EVER

    graybird78
    80 sg (old faithfull)

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    • #3
      Is it always the same routine? Is it always after running at highway speed, and then stopping?

      That seems like carb issues. Maybe it is flooding after running hard for a while, then stopping?? You might check the condition of the floats and needle/seat assemblies.

      If it is more intermitant than that, I would first look at the pick-up coil wires, then the coils themselves.
      The pick-up coil wires are a KNOWN weakness on our bikes, but are easy to check.
      There is also a history of bad coils. It is possible to have a coil that works fine at start-up, but fails when you get up to full opperating temperature.
      Look on the bright side. By the time that you diagnose the problem, you will probably know a whol lot more about your bike.
      Mike

      1980 SG "Angus"

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      • #4
        Runs Like Crap

        Just a suggestion, but an easy one to do. Open the fuel filler cap. Take an ice pick or similar tool and ream out the fuel cap vent. If you have air pressure available then take a blow gun and blow a little air up through the vent hole. It could be that you are getting a vacuum lock in the tank after high speed runs.
        Ken/Sooke
        78E Ratbyk
        82 FT500 "lilRat"

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        • #5
          Bikeboy, it's possible one of the carb slides is sticking.

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          • #6
            My vote is coils (including wires and caps), pick-up wires. If it gets hot and starts running on 2 cylinders, it is just enough time to heat up the electrical stuff. I don't think it carbs especially if it just started happening. The tank vent is a good check, mine would whistle when i parked in the garage, I had to open the vent back up. Weird problem.
            Gary Granger
            Remember, we are the caretakers of mechanical art.
            2013 Suzuki DR650SE, 2009 Kawasaki Concours 1400, 2003 Aprilia RSV Mille Tuono

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            • #7
              I'm with Gary on this one. Engine gets nice and hot, you're going at a good clip, the eind cooling the coils. Then you pull off to a stop and the hot engine cooks the coils, and bang, intermittent spark. If it was vacuum lock in the tank, it would happen at high speed.

              Here's a test the wife will love. Heat your oven to 150. Put coil in for 15 mins or until tender, then test with ohmmeter.

              Serve with cold beer. Good luck.

              Randy

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              • #8
                everyone elses diags. could be your problem but i will tell you what i had with my 79 xs11 special. i would ride it for a little while and all of a sudden i would loose half the engine, only running on two cylinders, for a littel while i could pull in the clutch and goose the throttle and it would go away, but i really got anoying and it cut out completely. so i decided to find the problem. it took me a couple of weeks to find it but insde the igniter box (that black computer under the seat) there are two trasistors, one for each ignition coil. one of those went bad and would randomly cut out on me. the way i found it was i had to cut the black plastic case off of the module and trace the circuit board, desoldered the one that went to the coil that would stop working i got one from radio shack (NOT THE RIGHT ONE) and put it in and the bike did run on all four cylinders, not well, but all did run so i knew that the igniter box would fix it so i got one from a junk yard $100 (dealer $400) and have not had a problem sence. not saying this is your problem but this happend to me
                Troy
                79' XS1100SF

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                • #9
                  Samw exact thing happened to my 79 standard, replaced black box, problem went away. Later 'Dog

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                  • #10
                    Bikeboy,

                    If you do trace the problem to the TCI box, for god's sake don't cut it open, mail it to me and I'll fix it for you. PM me for my address.

                    Randy

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