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Discussion Starter #1
I have a 2002 Thunderbird. Since I bought it a few months ago, I've noticed on rare occasion a slight "pop" when sitting at idle - felt it through the airbox covers more than heard it. THen suddenly on a 97 degree day, it started missing, backfiring, dying when trying to take off, etc. I let it cool off and got it home. I cleaned a very dirty air filter, cleaned the carbs, replaced plugs, though they didn't look too bad. Now it still misses a bit at idle, and when it warms up it will cough occasionally at certain speeds, and die when trying to take off. It sounded like a coil to me (cut out for a second), so I ordered one, but then I put a timing light on each plug wire and got erratic lights on each one, so unless they all 3 went bad at once, it must be something else. Is it the coil pickup? The expensive electronic unit? Or am I missing something else? Any input would be appreciated before I spend money I don't need to... I love my bike and wanna RIDE IT.:eek:
THANKS!
 

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Pickup coil or the igniter can act up at elevated temperatures, when they start to go bad. Coils can do that also.

Your symptoms sound more like the pickup coil to me.

But dirty pilot jets or some debris in the gas could also cause the same symptoms.
Did you remove the pilot jets and clean them so good that when you look at them with a magnifying glass the inside passage shines like brass? The pilot jets in the Keihin carbs like to be very clean...

Is the tank and petcock screens clean? The duckbill filter?

After cleaning the Petcock screena and duckbill filter, try some Startron that could do the trick.

Check all the connections to the coils.... clean with contact cleaner and grease with dialectric grease. tighten those connections with a gentle pinch from some pliars.

Just throwing out some things to double check before you spend money on ignition components.
 

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Sounds like a pickup coil, I just replaced mine had the same problems and now the bike works great. Then after that I replaced all 3 coils with Nology's and 3 new plugs the bike has never run better.
 

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A few things:
Check the clearance at the pickup coil.
(I don't have a book here with me for the spec)
Check the carb synch.
Check and clean all electrical connections.
This will include the ground wires for the run permissives.
(sidestand, kill, neutral switches etc.)
You may want to drain the carbs.
You may have some water in the bottom of the bowls.
If you ride on a level street in 2nd gear and try to hold a steady 3k rpm, what does the engine act like?
Any surging or popping?
After all this though, I won't be at all surprised if you do find a bad ignition coil.
(not pickup coil)
 

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If you ride on a level street in 2nd gear and try to hold a steady 3k rpm, what does the engine act like?
Any surging or popping?
Pardon my ignorance, but what is this symptomatic of? Bad ignition coil?

I have this issue but thought it was the carbs (since I'm running a very non-standard carb/airbox/exhaust set-up).

cheers,

~crosstie
 

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Pardon my ignorance, but what is this symptomatic of? Bad ignition coil?

I have this issue but thought it was the carbs (since I'm running a very non-standard carb/airbox/exhaust set-up).

cheers,

~crosstie
Usually an off idle stumble and miss that only continues to get worse over time where you lose that cylinder all together.
If you know what cylinder is acting up (and it's not number 1) switch the coil to the number 1 cylinder position.
If the tach starts to act up by dropping to zero intermitantly that's a sure sign of a bad coil.
I've had 2 go out before switching to Nology coils.
 

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One more thing that should be obvious but it's not; the balancer caps on the carbs. I had one fall off my T100 once and only realized it after I had spent an hour or so cleaning out the float bowls and jets, sparkplugs, etc.. It made the bike idle poorly and mis-fire and generally run like crap. You can get replacements at most autoparts stores.
 

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it's a 0.6mm air gap per the Haynes Manual, though i read on here someone doing 0.8mm to "better effect". Mine is set to .632mm since i just had to repair it, i broke it off the mount by accident :eek:
I tightend the gap up for better effect.
I was on the loose end of the spec and I adjusted it to the tight end of the spec.
Immediate improvement.
 

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Discussion Starter #12
Thanks, everyone! Now that it's been cooler, the bike runs just fine, the missing has gone completely, so it must be the pickup coil that is acting up when it's especially hot. I have one on order. The great part is, while I do the research like I have recently, I'm finding more ways to make it go FASTER! Like advancing the timing by opening up the coil pickup mounting holes to move it over a couple degrees.... And, I can't believe how restrictive the stock airbox is! So I couldn't leave that alone, drilled some holes to let it breathe.... now must jet the carbs, but already it runs like a very different bike - love it! That "induction roar" is really cool!
 

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Discussion Starter #14
the conclusion of the matter...

Well, I have definitively determined that it was the #3 coil gone bad. I had cleaned the carbs twice, cleaned the tank and duckbill filters, ran some Startron thru the tank, etc etc. I got my hands on a Nology coil and switched out each coil one by one until finally, on the 3rd coil, the symptoms immediately disappeared. A test of my patience for sure, but I learned a lot in the process, and thanks to all who contributed!
 
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