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41
The Motobrick Workshop / Re: 85 K100 ...all of a sudden backfiring and stalling when HOT! Still not fixed!
« Last post by Laitch on July 25, 2026, 05:21:23 PM »
Quote from: Atabeach on July 24, 2026, 05:08:34 PM
Thanks Laitch,  I will take your advice and change the alternator….
That isn't my advice.

The battery reading should be ≈13.5V to 14.5V with the engine running. Resting voltage should be 12.6V or above. Why do your battery's figures differ? My advice is to determine the root of each condition one step at a time. Why is your Brick's battery at 12.5V instead of within the optimal range. One case here where the battery wasn't holding a charge was caused by the alternator's cable connection to the battery being loose at the alternator side. Another case involved a bad diode.

All electrical connectors and ground connections of a 40 year-old Brick are first suspects when engine performance is erratic. The components themselves are the next suspects.

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The MBdotCOM Community Center / 2026 Beartooth Rendezvous, MT
« Last post by natalena on July 25, 2026, 10:43:37 AM »
It's getting close to the gathering of all makes and model's of motorcycling  .. except HD cruisers  :laughing4-giggles:

The 2026 Beartooth Rendezvous is August 14-17, at the Lion's Camp 10mi south of Red Lodge, MT.
Where else can you bunk 3 nights for 30 clams? Excellent dinner spread, this is a rally to gain weight on! Oh, and beer, that's  B-E-E-R, as there's no bear attacks nearby this season so far.

Hope to see some Bricksters there.
Register at Beartooth Beemers,  $100 pre Aug sign up.
* Resized_20250530_054230.jpeg (55.93 kB . 768x576 - viewed 66 times)
Cheers and Blessings
43
The Motobrick Workshop / Re: 85 K100 ...all of a sudden backfiring and stalling when HOT! Still not fixed!
« Last post by Atabeach on July 24, 2026, 05:08:34 PM »
Thanks Laitch,  I will take your advice and change the alternator….and move forward from there if there is no improvement….further, I was mistaken. I thought the alternator voltage at 13 would have been more than enough.
This model 1985 has a 33 amp alternator. Would anyone recommend a rebuild kit? Otherwise I am buying used off of Flea bay....
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The Motobrick Workshop / Re: 85 K100 ...all of a sudden backfiring and stalling when HOT! Still not fixed!
« Last post by Laitch on July 24, 2026, 03:27:02 PM »
Quote from: Atabeach on July 24, 2026, 03:04:09 PM
Am I mistaken to believe a faulty fuel regulator could cause a rich running condition? The temperature sender , TPS and coils seem to be fine. I’m just going with process of elimination. Does anyone think 13 volts is not enough to run the ignition system. Please advise.
I don't believe an alternator outputting 13V while the engine is running is capable of producing engine performance reliably.

Certainly, a fuel pressure regulator be a cause of over-fueling, but so can a clogged fuel return line, a faulty fuel pump or a faulty fuel injection control unit, not to mention the air flow meter which can be tested in place rather than on a bench. Repair using the process of elimination can be too costly for many of us; that's why there's all the testing; however, replacing parts also can eventually improve performance, if the defective part—or parts—eventually are replaced. That seems to be the diagnostic strategy with this Brick. AI can make a great companion for that.

45
The Motobrick Workshop / Re: 85 K100 ...all of a sudden backfiring and stalling when HOT! Still not fixed!
« Last post by Atabeach on July 24, 2026, 03:04:09 PM »
Am I mistaken to believe a faulty fuel regulator could cause a rich running condition? The temperature sender , TPS and coils seem to be fine. I’m just going with process of elimination. Does anyone think 13 volts is not enough to run the ignition system. Please advise.
46
The Motobrick Workshop / Re: 85 K100 ...all of a sudden backfiring and stalling when HOT! Still not fixed!
« Last post by Laitch on July 24, 2026, 02:59:39 PM »
Is something wrong with the fuel pressure regulator, or is it to be part of a feng shui reorganization?
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The Motobrick Workshop / Re: 85 K100 ...all of a sudden backfiring and stalling when HOT! Still not fixed!
« Last post by Edward on July 24, 2026, 02:54:30 PM »
Yes that is correct, the airbox and yes, he fuel pressure regulator is behind it.
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The Motobrick Workshop / Re: 85 K100 ...all of a sudden backfiring and stalling when HOT! Still not fixed!
« Last post by Atabeach on July 24, 2026, 02:44:19 PM »
The fuel regulator is behind it…am I using the wrong terminology again.? The black box thingy that holds the air filter….
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The Motobrick Workshop / Re: 85 K100 ...all of a sudden backfiring and stalling when HOT! Still not fixed!
« Last post by Laitch on July 24, 2026, 02:40:32 PM »
Quote from: Atabeach on July 24, 2026, 02:26:10 PM
While the airbox is out I will bench test the airflow meter.
….let me know if that makes any sense.
Is the airbox out now? If it isn't, why is it being removed?
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The Motobrick Workshop / Re: 85 K100 ...all of a sudden backfiring and stalling when HOT! Still not fixed!
« Last post by Atabeach on July 24, 2026, 02:26:10 PM »
She stars reliably, one shot. Idles rather smoothly…at 1k …anything below 1k she will stop running. When I hit gas she backfires and surges. She surges and cuts out when ridden. She constantly blows smoke.
My thinking:
Although 13 v is plenty…I’m going to change alternator as it is probably getting tired.
I have a used fuel regulator from a k75…I’ll change it
While the airbox is out I will bench test the airflow meter.
….let me know if that makes any sense.
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