BMW K bikes (Bricks)

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bobliu

bobliu
active member
active member
Hi all, been working on restoring a 1985 k100, and after a frame repaint, this problem has occurred, the bike would crank, and start for a second then dies, have made sure the battery is fully charged, and below is what I have tested. One thing I also realized before I put everything back together was there was some oxidation on the coolant temp sensor, so I sanded down the surface to make it shine again, not sure if it was the right thing to do.

1. Tested Hall Effect sensor using Crazy Frog's method and it was functioning properly
2. Tried starting the engine with the temp sensor unplugged, the engine started right away but was idling at 3k rpm, yes 3k, it was screaming
3. Tried switching the temp sensor out with a 1kohm resistor and the engine started right on with no choke and was idling at 1200 rpm. 
4. Made sure properly grounded all of the connectors, did continuity tests and resistance test between the ground wires and the battery, resistance was between 0.3-0.5ohm

5. Tested all plugs for spark, and all seem to be getting spark, but there's still occasional backfire from the exhaust.
6. There is white smoke coming from the exhaust when the bike is struggling to start, which may indicate a flooded engine? but the spark plugs are working, can it be running rich? 


Please give me any thoughts on what the problem can be! Thnx in advance



Last edited by bobliu on Sun Apr 26, 2020 10:23 am; edited 3 times in total

    

MartinW

MartinW
Life time member
Life time member
Did you apply thread tape or sealant to the threads of the temperature sensor. If you did this could be the source of your problem. The sensor is required to earth through the threads.


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K75s Hybrid
    

bobliu

bobliu
active member
active member
@MartinW wrote:Did you apply thread tape or sealant to the threads of the temperature sensor. If you did this could be the source of your problem. The sensor is required to earth through the threads.
I didn't, but I do think it's a ground problem tho

    

bobliu

bobliu
active member
active member
So I was able to get it running this afternoon but only when a little bit of throttle is applied, bike would still cut out with only choke open. Also I did recognize some white smoke and a little bit of back fire. I wonder if this can be due to the aftermarket exhaust I installed? I also checked the spark plugs and made sure all cylinders are getting sparks, but can the engine be flooded even with functioning spark plugs? A new temp sensor is on the way but it seems like the reading are correct, with both pins reading 2.5kohm at room temperature.

    

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