coil problems?

Discussion in 'Touring Models' started by brwdarr, Jun 16, 2010.

  1. brwdarr

    brwdarr Member

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    I have been chaseing a problem for 2 months now. the motor misfires at idle and low rpm. thought it was fuel related so I clean carb and jets and replace intake gaskets and carb gasket. sometimes it runs o.k. and sometimes it just doesn't seam to have any power. the exhaust has a different sound to it. well anyway, I check compression 150 in each jugs. sparkplugs looks o.k. a grayish color. I thought about the coil being bad, but I have never had a coil go bad, and I have wasted alot of money on coils though the years. the bike is a 1990 fltc with a 80 evo motor. I guess my question is how likely is it to be a bad coil? are hd coils known to go bad. any other suggestion would be appreated.
     
  2. glider

    glider Veteran Member

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    What about plug wires? Tried a new set of plugs?

    Look at the coil for possible carbon tracking (arcing to ground) It looks like a pencil line or crack in the housing which indicates a misfire.
     
  3. Hoople

    Hoople Account Removed

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    If your in 3nd gear cruising at 2,000 RPM and you roll hard into throttle (WOT) will the bike pull clean and smooth to redline without ANY misfire? Will the same happen using 4th gear.
     
  4. brwdarr

    brwdarr Member

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    I have change plugs and wires. bike pulls good at {wot}. I had the coil off and didn't see anything wrong with it visibly. no cracks. at 2000 rpm, if you try to ease back on the gas it will skip and stumble a little bit. give it more throttle and it is fine. sounds like a slow jet problem right? I bought a new slow jet #45 and install it. also I adjusted my idle mixing screw out a 1\4 of a turn. help some, but skip is still there. right now it's running pretty good, but in a day or 2, i'll hop on it and it will run like a slug. like the timming is off or a jet is clog or something like that, and i'll tear back into it again. could it be bad gas? I ran through 3 tanks of gas from different station and added some seafoam to each tank.
     
  5. glider

    glider Veteran Member

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    Sounds like a fuel delivery problem now. Have you checked the delivery of the accelerator pump and also the diaphragm on the slide for holes or tares.
     
  6. brwdarr

    brwdarr Member

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    yes I've have check both. seams ok to me.
     
  7. Hoople

    Hoople Account Removed

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    If you experience NO issues during peak combustion pressures, my guess would be you have ample spark reserve during idle. It's not 100% proof positive but it carries a LOT of credibility.

    Peak combustion pressures usually place 50% more demand on the secondary loop. The secondary loop consists of the coil (secondary side only) /wires/plugs/plug gap/etc.

    If what you say is true about WOT performance, then I feel you can discount an ignition issue.

    Glider's path is the road you want to take. Maybe even intake leak check with propane. (?)
     
  8. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    I had an intermittent problem like the one you describe on my '91 Dyna. Turned out to to be an almost invisible cut in the spark plug wire insulation where the wires come out of the coil cover going to the plugs. The only way I finally found it was when it bit me one day while I was searching for the problem somewhere else!! Cheap quick fix is just to replace the wires and make sure there is no contact with the coil cover.

    Looking above, I see you have done that.

    With the worry about gas, have you drained the tank and removed the petcock and strainer to see if it is all clogged up? I finally just replaced mine after trying to clean it a bunch of times. Used the Pingel Power Flow valves (Power-Flo™ Fuel Valves).

    TQ
     
  9. tourglider

    tourglider Member

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    The coil can be checked for resistance with a multi meter. Don't know what an 80 should should read but 84 to 88 should read,primary coil 2.5-3.5 ohms, secondary, 11250-13750 ohms. Also check cam sensor they can do some goofy things. with engine running spray with electrical cooling spray,then heat with hair dryer. If engine changes replace. I chased the same problem and found it to be the cam sensor. good luck
     
  10. Hoople

    Hoople Account Removed

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    Does this bike have VOES spark advance..