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  • #1

    Low Compression/No Spark

    I just bought a 79 XS1100 Special. It is not running so I started doing some troubleshooting. I get spark only on cylinder 1, but, only when I release the starter button. I have verified that there is 12.7V on the battery (so the ignition should be firing) and the plugs are fresh.

    I am getting fuel as I had a backfire from cyl 1 and there was a strong smell of gas.

    I checked the compression and it is 145/155/70/130 with the compression on cyl 3 going to 155 after a teaspoon of oil was added.

    As far as the compression I think that the rings need to be replaced (based on what the Clymer manual said).

    I have a complete replacement wiring harness that I just bought and plan on switching in this weekend (as the old one has been hacked to death), but I would like to hear what else I need to do for troubleshooting. Thanks.
    79 SF 3H3 Engine, 145/45 Mikuni Jets, El Cheapo Pod Filter Mod w/ EMGO Pods, Coil Repower w/ Dyna Coils, Accell Wires and Side Gapped Plugs, 78 Mech Advance, 4-2 Turnouts
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  • #2
    Check your coils; the wire ends on the stock coils go bad or can be connected poorly and that will affect the spark. Remove the coils, unscrew the ends off the wires and then check resistance through the secondary (spark plug) side of the coils. Should be about 15K ohms. Each plug wire end should read about 5K ohms. If the ends are bad, they can be replaced for about $4 each. You can also find that the wire ends can be corroded, cutting about 1/4" off will help expose 'cleaner' wire.

    And before you assume that the rings are bad, check your valve lash; too tight on a valve will give a low compression reading. On these bikes, the clearance gets less as things wear, not more.
    Fast, Cheap, Reliable... Pick any two

    '78E original owner - resto project
    '78E ???? owner - Modder project FJ forks, 4-piston calipers F/R, 160/80-16 rear tire
    '82 XJ rebuild project
    '80SG restified, red SOLD
    '79F parts...
    '81H more parts...

    Other current bikes:
    '93 XL1200 Anniversary Sportster 85RWHP
    '86 XL883/1200 Chopper
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    Yep, can't leave nuthin' alone...

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    • #3
      I would certainly get the bike running and put some miles on it before jumping in and replacing the rings. Most likely rings would loosen up and reseat after some time. I really regret jumping the gun and replacing the rings in mine.
      Nathan
      KD9ARL

      μολὼν λαβέ

      1978 XS1100E
      K&N Filter
      #45 pilot Jet, #137.5 Main Jet
      OEM Exhaust
      ATK Fork Brace
      LED Dash lights
      Ammeter, Oil Pressure, Oil Temp, and Volt Meters
      Green Monster Coils
      SS Brake Lines
      Vision 550 Auto Tensioner

      In any moment of decision the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.

      Theodore Roosevelt

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      • #4
        So there's your problem...

        It's always the easiest answer isn't it?

        The leads for 1 & 4 were broken at the base, so now time to replace the coils and plugs.
        79 SF 3H3 Engine, 145/45 Mikuni Jets, El Cheapo Pod Filter Mod w/ EMGO Pods, Coil Repower w/ Dyna Coils, Accell Wires and Side Gapped Plugs, 78 Mech Advance, 4-2 Turnouts

        Comment

        • #5
          I agree with checking the valve lash. I've bought 2 of these bikes seized up and they ran great after breaking the engine loose and adjusting things. It will be fine.
          "The Hooligan" XJ1100, Virago Gauge Pods, Screaming Eagle Mufflers, K&N Filter, hand made rear fender, side covers, and solo seat, round bar conversion, small headlight, tail light, and cat eye turn signals, chip fuses, rewired the right way.

          Pics: http://s1236.photobucket.com/user/ya...?sort=6&page=1

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          • #6
            Brand New Coils

            So I just installed brand new coils and I have the same problem. It will not spark while cranking, but as soon as I stop I get one spark from #1.

            Also just put in a brand new battery, so the TCI should be getting the voltage it needs.
            79 SF 3H3 Engine, 145/45 Mikuni Jets, El Cheapo Pod Filter Mod w/ EMGO Pods, Coil Repower w/ Dyna Coils, Accell Wires and Side Gapped Plugs, 78 Mech Advance, 4-2 Turnouts

            Comment

            • #7
              So I got it running for a split second, but I shut it off because I had just rigged up the coils to see if they would work. Turns out that the battery wasn't providing enough power to the TCI.

              But now the terminals on one of the coils broke off and no amount of super glue would fix it. So now I have to wait for a replacement.

              Has anyone else had this happen with the coils from MixeXS?
              79 SF 3H3 Engine, 145/45 Mikuni Jets, El Cheapo Pod Filter Mod w/ EMGO Pods, Coil Repower w/ Dyna Coils, Accell Wires and Side Gapped Plugs, 78 Mech Advance, 4-2 Turnouts

              Comment

              • #8
                A lot of people have had nothing but trouble with MikesXS coils. I would think about finding a good factory set and return those if you can. I'm sure more will chime in soon on that.

                You can also get coils for an XJ550 as well. There were several 4 cylinder model Yamahas during the early to mid 80's.
                "The Hooligan" XJ1100, Virago Gauge Pods, Screaming Eagle Mufflers, K&N Filter, hand made rear fender, side covers, and solo seat, round bar conversion, small headlight, tail light, and cat eye turn signals, chip fuses, rewired the right way.

                Pics: http://s1236.photobucket.com/user/ya...?sort=6&page=1

                Comment

                • #9
                  Hey Spayne,

                  Perhaps you didn't read thru the tech tips....we have notes about the MikesXS coils that many of us tried a few years ago...the cheaper black ones first, and then the stronger green ones. The black ones fry themselves around 10k miles, the green ones are expected to be a bit later but a few have reported problems with them as well. Mikes doesn't provide any warranty on their coils either!!! You'll be lucky if you're getting Mikes to provide a replacement. As stated a variety of coils will work on our bikes, but if you're planning on keeping your bike, then you may want to pony up the $$ and make the investment in some actual DYNA-TEK brand coils. They provide 35+ KV output, have a 1 year warranty, do not require the ballast resistor...needs to be bypassed for full power, makes for easier quicker starting, strong running especially at low rpms because of much stronger spark energy at the low charging voltage rpm range.

                  T.C.
                  T. C. Gresham
                  81SH "Godzilla" . . .1179cc super-rat.
                  79SF "The Teacher" . . .basket case!
                  History shows again and again,
                  How nature points out the folly of men!

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                  • #10
                    I just installed the DynaTek coils, but it is still not starting.

                    I am getting a few backfires and #2 is sparking but not #1. I think it might be a low battery, but it does the same when I have it hooked up to a charger on 12V at 6A. Also the voltage doesn't seem to drop below 11 with the charger on. The sparks only seem to happen after I stop pressing the starter.

                    Question: The instructions for the coils said that they have no polarity and I can hook up the primary wires in any order, but I assume that they have to be identical on both coils. Could someone clarify this for me?

                    Since I am getting occasional spark does that mean that my TCI is good? I am really scared that I may have fried it messing around with the last set of coils.
                    79 SF 3H3 Engine, 145/45 Mikuni Jets, El Cheapo Pod Filter Mod w/ EMGO Pods, Coil Repower w/ Dyna Coils, Accell Wires and Side Gapped Plugs, 78 Mech Advance, 4-2 Turnouts

                    Comment

                    • #11
                      As for the DynaTek coils, all they are is a fancy electromagnet with a bunch of extra wire(secondary) wrapped around the primary windings which are the primary electro-magnet. It will make a magnetic field no matter which direction the current is flowing thru it, that's why they said there's no true polarity, just as long as you have 1 positive and 1 negative so current flows thru the primary circuit then you're good!

                      It's possible for the TCI to be fried, but you really need to look at the PickUp Coil wires under the left crank cover...see the tech tips for photos and techniques. No fire from #1, you probably aren't getting any fire from #4 either because they are paired in the coil, and the pu coil triggers each coil which controls 2 plug wires at the same time....they fire with a wasted spark design....timed to fire both during the power portion of the stroke and also the exhaust portion....the coil fires both wires at the same time.

                      When you're trying to start the bike power is going to the spark plug coils, the primary coil gets energized, but either the PU coils are not triggering the TCI....or the TCI is not responding to the PU coil signal....so either way, no spark....UNTIL you stop trying to crank or turn off the key, then the power in the spark plug coil primary collapses....and that's when it creates the spark in the secondary windings that go to the plugs.

                      Just also checking..you did bypass the ballast resistor didn't you?

                      T.C.
                      T. C. Gresham
                      81SH "Godzilla" . . .1179cc super-rat.
                      79SF "The Teacher" . . .basket case!
                      History shows again and again,
                      How nature points out the folly of men!

                      Comment

                      • #12
                        How much power is getting to your coils when your starter motor is engaged? I wonder if it's possible that your starter motor is sucking too many amps. Now I see why you wanted the kick start parts, I'll get on that this weekend. It may be worth it to just start cleaning all your grounds and power wire connections. Sounds almost like a power distribution problem to me. If you have enough weak connectors in your harness, then they will all take their tole on energy consumption.
                        "The Hooligan" XJ1100, Virago Gauge Pods, Screaming Eagle Mufflers, K&N Filter, hand made rear fender, side covers, and solo seat, round bar conversion, small headlight, tail light, and cat eye turn signals, chip fuses, rewired the right way.

                        Pics: http://s1236.photobucket.com/user/ya...?sort=6&page=1

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                        • #13
                          Yeah, everything is pretty corroded, so I think I will try getting the new 4 ga wires and starter solenoid on this weekend, and maybe try cobbling together a wiring harness.
                          79 SF 3H3 Engine, 145/45 Mikuni Jets, El Cheapo Pod Filter Mod w/ EMGO Pods, Coil Repower w/ Dyna Coils, Accell Wires and Side Gapped Plugs, 78 Mech Advance, 4-2 Turnouts

                          Comment

                          • #14
                            The starter solenoid shouldn't be bad unless it freezes up. I would just start cleaning crimping, soldering. Don't spend any more money on components until you are sure your wiring harness is in good shape.
                            "The Hooligan" XJ1100, Virago Gauge Pods, Screaming Eagle Mufflers, K&N Filter, hand made rear fender, side covers, and solo seat, round bar conversion, small headlight, tail light, and cat eye turn signals, chip fuses, rewired the right way.

                            Pics: http://s1236.photobucket.com/user/ya...?sort=6&page=1

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