R100RT funny stumble

Discussion in 'Airheads' started by pkboxer, May 19, 2012.

  1. pkboxer

    pkboxer Been here awhile

    Joined:
    Jun 15, 2011
    Oddometer:
    102
    Location:
    cincinnatus oh
    Buddy has an '84 R100RT. After riding 150 miles the bike started dying suddenly.

    He could keep riding by turning off the ignition switch and then back on and it would seem to run fine while it was running but then die again.

    and it would occasionally have a nice back fire.

    Seemed to have fine flow of fuel, plugs looked good.

    The idle was just slightly rough.

    Thought it was heat related but we let it cool overnight and the problem was still there.

    Battery was nice and strong. Started the bike several times and starter spun quickly.

    What are the symptoms and checks for a bad ICU?

    My bike has points!
    #1
  2. ignatz72

    ignatz72 call me iggy

    Joined:
    Aug 6, 2010
    Oddometer:
    626
    Location:
    Mid-South, M-town
    Is this bike new to your buddy? How many miles on it?

    Plugs checked? Plug wires tested for resistance and checked for cracks? ICU been separated from the heat sink and new heat sink paste applied recently? Coils tested for continuity/resistance?

    There are voltage tests that can be done to the ICU (in the Clymer's manual at least), but it's rather difficult to describe here. The Clymer actually has pretty good electrical tests for coils/wires/ICU. Unfortunately the only real test for an intermittent ICU problem is to plug in a known good one. Pretty much the same for coils and plug wires (at least plug wires are fairly cheap).

    Have any of these items been replaced recently? Double-checking connections and making sure plug wires are fully seated in the coils might help.

    You could pull the plugs and ground them on the head to check the spark, but as others have said here before, the eyeball can't tell the difference between a strong spark and a weak one. You'll only be able to tell if one isn't regularly firing. If that's the case, it's either that coil, that plug wire, or the ICU.
    #2
  3. pkboxer

    pkboxer Been here awhile

    Joined:
    Jun 15, 2011
    Oddometer:
    102
    Location:
    cincinnatus oh
    Bike has been owned by him and his dad since new. Milage is unknow to me, guessing about 60k

    Only recent change was new plugs.

    We reseated the wires and cleaned up the connections but now change.

    Thought maybe the fact that it would die but them come back to life after turning the ignition off and back on would set off bells for someone.:ear
    #3
  4. supershaft

    supershaft because I can

    Joined:
    Sep 9, 2010
    Oddometer:
    9,116
    Location:
    San Francisco Bay area
    If it has the original crack-O-matic coil chances are that is the problem. Other than that it could be anything or a combo of anythings. I test bean cans with a LED light but they can test good and still be bad. Coils can test good but still be bad. I think plug wires and spark plug caps test pretty much straight up. It seems that not too many people mention the caps. I see the caps acting up way more often than the wires. That and them not being plugged into the coil right.

    150 miles? Is it out of gas and then starts up after putting it on reserve? Just joking but it really could be anything! :D

    Never mind the coil info!! Wrong model!!
    #4