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Discussion Starter #1 (Edited)
I have a 1992 K100 RS. It runs good at an idle and good up to 3,000 RPM. From 3,000 to 4,500 rpm it surges very noticeably. After 5000 it runs smooth again. Here is what I have done so far.

Replaced all plugs and two wires
Replaced all vacuum caps
Checked for air leaks, and checked vacuum hoses
Synced the throttle bodies
Good fresh fuel
Valves were checked a few months and very few miles ago by Max BMW

I am thinking it might be a weak coil, does that sound right?

Thanks for you thoughts!
 

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Discussion Starter #3
owrstrich said:
if it were my motobrick i would replace the fuel filter... clean up the motronic connector... clean up the under tank 4 pin fuel pump connector... then ride it till it wont move...

j o
I will look at that, the fuel filter is fairly new as the bike was bought last year with a bad fuel pump and a new pump and filter was installed and the connecter checked.

Where is the motronic connector located?

Thanks for your input!
 

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Check the throttle potentiometer adjustment: Pull the boot away from the 'pot and find the white/pink wire. With a straightened paper clip. probe the connector at the 'pot with the ignition lock turned to run and attach a digital multimeter. It should read about .380-.400 MV. If not, loosen the socket head screw that hold it and adjust accordingly. This is a fine adjustment and it may take several tries to get it right.
 

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PsyKotic Waterfowl
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54089093 said:
Check the throttle potentiometer adjustment: Pull the boot away from the 'pot and find the white/pink wire. With a straightened paper clip. probe the connector at the 'pot with the ignition lock turned to run and attach a digital multimeter. It should read about .380-.400 MV. If not, loosen the socket head screw that hold it and adjust accordingly. This is a fine adjustment and it may take several tries to get it right.
MV is an abbreviation for Megavolts. 0.380 MV = 380,000 volts.

I think .0.375 volts might be a better target - measured between pins 1 and 4 at the TPS connector with the throttle at idle position..
 

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Discussion Starter #7 (Edited)
Update: Completed the following this morning.

New fuel filter installed and new fresh gas.
Adjusted TPS to .375 volts
Cleaned the motronic connector
Checked the fuel pump connector

None of these things made any difference.

Went to put new heat sink compound on the ignition amplifier and mine is attached to the battery box without screws, it mounted on long studs. I got it off but I was removing the battery box and broke one of the rubber mounting studs so now I have to wait to get a new one to see if the new heat sink compound makes any difference.

I don't really know where to go next.
 

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I am wondering why you replace two plug wires and not 4. You can buy aftermarket sets for the price of one BMW wire.

In any case did you do the Ohm readings on them to check them? They should all be in the 5K range. I have the almost same wires on the K1200RS, did the readings and two of the wires were showing and then not showing. :wtf: Drove me nuts for a few minutes til I realized that they were reading when bent similar to the operating position and then laid flat....no more readings. :) Had to look back to my youth to remember that but typical carbon wires problems when the carbon core is compromised. All replaced with copper core.
 

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Discussion Starter #9
I replace two wires because they would vibrate off with time. I just ohmed the other two and they both came out to six ohms. The readings are still there when I bend the wires so I think they are good. Thanks for the ideas I like the way you think!


Update:
Installed a new ignition module with new heat sink compound and still no change. Does anyone know what the specs are for the coolant temp sensor and the air temp sensor so I can test them?
 

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Discussion Starter #10
Update: When I left the bike the fuel pump would not run as the computer would not ground the fuel pump relay, (same wire supplies power to the injectors) tonight it all worked great again with NO PROBLEMS for a while then the breaking down in the 4-5k rpm range and then finally when I rap on the computer it died completely again. I had already cleaned all connections too. It would not die wiggling the wires so I am pretty sure it's the computer, now to find one.....
 
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