85 K100 ...all of a sudden backfiring and stalling when HOT! Still not fixed!

[Edward]

Yes that is correct, the airbox and yes, he fuel pressure regulator is behind it.

[Laitch]

Is something wrong with the fuel pressure regulator, or is it to be part of a feng shui reorganization?

[Atabeach]

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.

[Laitch]

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.

[Atabeach]

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....

[Laitch]

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.

[Atabeach]

Laitch:
  The battery and grounds were removed cleaned and reinstalled…reply 1 ( Bike was sitting for a decade and all electrical connections were removed& cleaned.)
The battery…at 12.5 was tested using my battery load tester…showed good…re- assess as needed, 4 months old…

…The bike always seemed to charge and start right up. I never thought to test the charging system, when I did I still thought 13 Volts was sufficient to run…ignition. Guess it may not be.
  So....now, I removed and bench tested alternator ( to clean all brushes & contact areas also )
Turns out she is tired. Ohms across the two brass armature rings should be 2.5….they read 5
 Changing the original 40 year old alternator makes sense…as did the temperature sender ( ohm reading not perfect) and hall sensor….not big ticket items.
The coils and wires checked out ok and were not replaced.
  I am following a logical order here not haphazardly changing stuff.
This is a $750 barn find…so I was expecting some costs….It still has the original fan!
 
Thanks for your …..help. 😳😳

[Atabeach]

So the alternator was changed I am getting a solid 13.7 at around 2500 rpms. Battery was swapped with my other bike...no difference. I changed out the fuel regulator (used) no improvement....The bike always starts right up and idles smoothly at 12/1300 rpm. It backfires when revved or put under load by riding. It smokes at all rpms and all the plugs are still wet with gasoline.

[Edward]

I wonder if your coolant temp sensor is faulty, causing the ecu to think the engine is too cold therefore pumping more fuel than needed? I don't recall but did you adjust your bleed screws to have a in-sinq throttle body?

[Atabeach]

The temperature sensor was changed.  I have not adjusted the screws because the bike was running fine…This happened suddenly. Thanks

[Edward]

tps reset?