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Thread: Time for new Hall sensors on my 1985 K100?

  1. #1
    Registered User tonysuburb's Avatar
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    Time for new Hall sensors on my 1985 K100?

    It happened again yesterday when the weather was hot. I was running my K100 at about 70 miles per hour and then it started to stumble and then shut down. It was almost like it was running out of gas. I pulled over to the side of the road and waited 10 minutes, then it started up again. I have been reading about the Hall sensors and thought that may be the problem. Is there any way to install the sensors by splicing them into the old wiring?

  2. #2
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    When I had a similar problem with my K100, it turned out that the ignition switch needed cleaning. If you haven't cleaned the switch, you may want to try that.

    If you're going to replace the sensor assembly, the connector is under the gas tank near the radiator cap. I don't know if the individual sensors are still available, but, years ago I purchased two sensors, removed the original rivets and sensors, soldered the new sensors and reinstalled them on the plate.

    Regards,


    Richard Flood
    Last edited by richo2006; 07-04-2020 at 01:41 PM.

  3. #3
    Dances With Sheep GREGFEELER's Avatar
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    Quote Originally Posted by richo2006 View Post
    When I had a similar problem with my K100, it turned out that the ignition switch needed cleaning. If you haven't cleaned the switch, you may want to try that.

    Regards,


    Richard Flood

    I would strongly suggest that you do a range of tests before assuming the Hall Effect sensor is the cause. They are *very* reliable, and with a bike that is 35 years old, there is much potential for oxidized electrical contacts. The ignition switch is one well known one, but also the contacts on the engine and fuel computers, and even the connectors under the gas tank.

    My first K-bike was a 1996 K100RT which the previous owner was selling because it would just stop randomly once the temperature was 70 or above. After about 10 minutes it would start and run fine until the next time. She had done everything the Internet suggested to no avail, and the bike wouldn't act up when she took it to a dealer. I figured, hey, it's K-bike - they *want* to run, so this has to be something relatively easy to fix.

    After much troubleshooting, I tested if juice was reaching the fuel pump during a failure. Sure enough not. The problem was that the ground wire tab spot welded to the underside of the fuel sender had become corroded just enough to open up once it got hot enough, hence the 70 degree threshold. A new fuel sender unit completely cured it, but I figure that as a very weird and unusual problem.
    Greg Feeler
    Ambassador & amateur K-Bike collector, it seems
    1972 R75/5, 1990 K75, 1990 K1, 1992 K75S, 2003 K1200RS

  4. #4
    3 Red Bricks
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    Tony!

    If you truly suspect the hall effect sensor, remove the T shaped sensor cover, ride around the block a couple times to warm up the bike so that it will idle smoothly. Bring it back and run a hair drier pointed at the sensor while it is idleing. The heat will cause a failing sensor to act up.

    But, I agree with Richard and Greg. It is much more common that the problem is dirty ignition switch contacts, dirty kill switch contacts, or bad fuel pump connections at the tank connector or the tank through plate.


    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
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  5. #5
    Registered User tonysuburb's Avatar
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    tested Hall effect sensor today

    I removed the cover and ran a hair dryer on the Hall effect sensor after the bike was warmed up. No sputtering or stalling. There was a misfire every now and then so I checked the instrument panel and saw that my charging light was blinking on and off. Is it possible that the charging system is the culprit?
    Last edited by 98lee; 07-06-2020 at 02:09 PM.

  6. #6
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    Tony,

    Probably not. You probably didn't have the rpm high enough for the alternator to be charging fully.

    Put a volt meter across the battery terminals (if you have a charging pigtail for a battery tender, you can measure it there). Check the standing voltage, then start the bike. Check the voltage at idle and then check it as you bring the rpm slowly up to around 3000 rpm. At somepoint before 3000 rpm, the voltage should jump from the standing voltage to above 13.5 volts.




    Last edited by 98lee; 07-06-2020 at 09:55 PM.
    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  7. #7
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    My Ď84 KRS stopped running two years back, then started, then quit, then started, limped home. It was the NLA fuel pump electrical connector. Removed the plug, carefully pinched the thingees, hasnít happened since but in the memory bank. Will go to plan B if needed.

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