Chrysler exonerated; Rusty indicted

[Rusty Bucket]

So as those on last night's ride know, my 650 Yamaha with the Chrysler electronic ignition quit last night pulling into the Bonnet Hill pub, and resisted all attempts at restarting, including a two hour session afterwards at the shop.  I persisted with attempts to get it to run again because it still had an admittedly intermittent and weak spark.  It would not even cough, though.  So today I changed out the coil, which bench tests exactly the same (2.8 ohms primary, 24k ohm secondary) as the coil I put in.  The bike fired immediately and works just as it did.
  Now, the question is, how does a coil fail and still bench test as well as one that actually DOES work?  And is the failure due to my ignition, or was it just that coil's time?  The failed coil had about five thousand miles on it;  it's the only one I have ever had on the bike.  I am thinking of increasing the resistance on the supply side of the ignition box, but I can't see that prolonging or easing the life of the coil much, and the primary resistance of the coil is similar to what Chrysler had in mind for it's ignition, though it only fires 1/3 as often.  Any conjecture or opinions welcome.

[Kaw-meister]

The resistance of the coil is a protection for the ignition from the power of the coil. for example , if you put a non-resisted coil into a points ignition system and roll it till the points contact, and leave it sit there. it will melt the wiring and cook the points. also when running, the more spark in your points, the faster they deteriorate. now the coil issue where it didn't work then bench tested well, sounds like you may have had a bad connection in your wiring system(and wiggling the wires solved that for now). or some times a coil will quit working when they get hot(things expand and contract with temp change). and of course could bench test well if bounced around a bit just right.
hope this helps

[madmac74]

  I had a Dyna 3 Ohm coil die on me a few years ago , and I chalked it up to overheating, Like  the Miester said. I did the same test as you did Russ, but it ended up having hairline cracks in the coil casing itself...

Glad to hear Chrysler wasn't to blame. But ya still should have an extra ballast resistor with you!!!!! ( if ya need one )

MAC

[Rusty Bucket]

I went around the shop last night digging out ballast resistors from all the places they collected.  I found 6, I think.  All the single rail ones are 1.7 ohm ones, and the duals have a 5 ohm strip.  5 seems a bit much, but I am thinking I might see how the 1.7 would affect the starting of the bike.
  When I removed the tank to look at the coil, I thought I was seeing chafed areas on the primary wire's insulation, places where it might have been rubbing against the mis-matched tank, but there was no conductivity there, it was just dirt.
  True enough I haven't heated the coil with a blowtorch, or hose-clamped it to an air hammer while conducting resistance tests :  the coil had ample chance to mend it's ways at the shop, having had it's wiring disconnected and examined, poked and prodded.  The last good spark it produced was 10 ft from the Bonnet Hill parking lot, and it hasn't produced another worthwhile one since.
  The primary resistance of the Yamaha dual-output coil is 2.8 ohms,  I would have thought that would be conservative, most electronic ignitions from that period presume a resistance of about half that in their matching coils.  I can buy dual-output replacements for about $35, but they almost never give the impedance values.