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Author Topic: bike was running fine, now won't start (cranks but no spark)  (Read 513 times)

Little_Joe

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Hello, My '04 comet has been sitting for about 3 years.  I recently got it out and after installing a new battery, draining out old fuel, and inspecting entire fuel system (carbs/fuel filter were clean), I put some new fuel in it and got it running.  I started it a few times over the next few days and let it warm up till I was satisfied it would start and idle reliably.  Four days ago I got home from work, started the bike (it started right up) and tried to move it up a ramp (had to go up three steps to street level). The ramp slipped so I backed the bike back down and shut it off.  From then on it would not restart.

Batter voltage was 12.8-12.9; starter cranks; fuel getting to carb float bowls.

Basic troubleshooting has revealed no spark in either cylinder.  Ignition coil resistance measurements are 1.9 ohms on the primary and 15.2k ohms on the secondary (book says .19-.24 and 5.4k-6.6k) so my resistance values are out of spec.  I get the same higher than spec values on the stator (the book calls it the charging coil.)  It is supposed to be .6-.9 ohms between any of the three wires and I am getting 3.8 ohms.  I tried measuring resistance values on the CDI based on the chart in the book, but get nothing close to what it says, most have no continuity.  I have a hard time believing that the ignition coils, stator, and CDI all failed at the same time.

The way the bike started right up and ran fine then after being turned off has no spark makes me think I'm missing something really simple but I am at a loss....After not riding for 3 years I am itching to back in the saddle!
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Christmas

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Re: bike was running fine, now won't start (cranks but no spark)
« Reply #1 on: July 07, 2017, 05:38:02 AM »

Those 3 are all linked so I could see that they'd all fail if they were fried by the reg rec failing?

I think the primary on the coil reading is right, it's usually around 3ohms on most bikes so I think that .19-.24 is a typo and its meant to be 1.9-2.4? But 15.2k is WAY out of whack.

I've got no idea how much you know so I'm going to ask.. How did you check spark?
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Little_Joe

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Re: bike was running fine, now won't start (cranks but no spark)
« Reply #2 on: July 07, 2017, 05:45:50 AM »

Quote
How did you check spark?
Grounded spark plug on cylinder head...tried both cylinders, and swapped plugs between cylinders.

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albertinhouston

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Re: bike was running fine, now won't start (cranks but no spark)
« Reply #3 on: July 07, 2017, 01:14:34 PM »

CDI maybe.
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Little_Joe

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Re: bike was running fine, now won't start (cranks but no spark)
« Reply #4 on: July 07, 2017, 10:04:51 PM »

Update:  While checking to see if I was getting voltage to the from CDI to ignition coils the rear coil gave me a negative reading that slowly ticked down to 0.00. 

On a hunch a tried starting, and bike started right up!  I let it run for a about 10 min. then tried a test ride in the alley.  I made it about a half mile till it stalled out and would not restart.

Checked battery voltage after stall and it was good at 13.0.  Rear ignition coil gave the same negative reading that slowly bled down to 0.  Still no-go on starting.

I now believe that my problem is in the ignition coil.

Any further input is greatly appreciated!
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Little_Joe

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Re: bike was running fine, now won't start (cranks but no spark)
« Reply #5 on: July 17, 2017, 02:23:33 AM »

Old spark plug caps had a resistance of over 9k ohms.  I ordered and received NGK plug caps.  These have a resistance of 4.9k ohms.  I installed the new caps on existing coils and then in bike.  After a few min. of crank...wait....crank...wait the bike started, revved when I gave it a little throttle, and stalled out when I let off the throttle then wouldn't start again.  I changed out spark plugs for brand new and was able to start the bike, but now the front cylinder is not firing and my tach is dead.  I pulled the front coil back off and everything tests as it did when I installed the new cap.

I quit for the evening, but tomorrow will swap coils.
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