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  1. #1
    Registered User harryhendo's Avatar
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    1987 R80 rough running above idle

    Hi Folks,

    My 1987 R80 (which I bought new in 1987) was sitting in a barn for 10 years, and I've been getting it back in shape. That meant rebuilding the Bing carburetors and also clearing out the mice damage to the airbox. There were also some frayed/nibbled wires, which I replaced.

    The bike starts and idles just fine, but when I increase RPMs to around the 3000-5000 rpm range, it runs roughly, surging and skipping.

    I tested the battery's output (which is 12.5 volts, normal), and the voltage delivered to the ignition coil's #15 terminal (11.8 volts), which seems fine. I then tested the voltage between pins 2 and 4 of the ignition amplifier (the black module mounted on a heat sink with 6 inputs) with the ignition ON, and found the voltage to only be 3 volts with the ignition amplifier connected to the wiring harness and also when I tested between the connectors on the disconnected wiring harness. That voltage is very low.

    Any idea where I should look to find the issue? The wiring diagram in my Haynes manual is not very helpful.

  2. #2
    Liaison 20774's Avatar
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    You didn't mention doing a carb synch after rebuilding the carbs. If that wasn't completed, could be that the carbs are not pulling evenly at elevated RPMs.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Registered User harryhendo's Avatar
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    Quote Originally Posted by 20774 View Post
    You didn't mention doing a carb synch after rebuilding the carbs. If that wasn't completed, could be that the carbs are not pulling evenly at elevated RPMs.
    Yes, sorry for the omission. I did do a carb sync with a TwinMax sync tool, and the carbs are pulling evenly at 3000 rpm, where I tested, as well as at idle (1100 rpm).

  4. #4
    Day Dreaming ... happy wanderer's Avatar
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    Start by measuring the resistance (Ohms) by removing both plug leads and measuring the resistance between them. You should see around 21K ohms (from memory..) If you don't then test both plug wires one at a time. Normally they are 5K ohms because the caps have 5K resistors in them. If all these things check out and you know the plugs are new and OK then your coils, wires and plug caps are OK. This means the ICU (Ignition Control Unit) which I think is what you are describing may be flaky. It is mounted on the backbone under the tank on a heat sink and it might be the problem. If not serviced the heat sink paste dries out and the unit will overheat causing it to become flaky at first and finally it will fail completely. The other thing in this circuit is the Bean Can which has a hall effect sensor in it and they are known to fail with heat and time eventually. Testing them requires some equipment most don't have and usually a test jig so swapping with a known good used one is my approach here.

    Never change more than ONE thing at a time when you do this sort of testing and then do your baseline test (run the bike at 3K RPM) and see if anything has changed for every part change you make.

    You should also be checking everything you touch for corrosion. Corrosion in the coil output is common on these bikes and can cause high RPM missing. Loose connections or corroded connections also. Make sure your battery ground is perfect as well.
    Last edited by happy wanderer; 01-14-2019 at 09:08 PM. Reason: spelling...
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  5. #5
    Registered User harryhendo's Avatar
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    Excellent! Thanks Happy Wanderer! I have some homework to do tonight...

  6. #6
    Registered User Guenther's Avatar
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    Did this happen BEFORE you rebuild the carbs?

    One guess would be the diaphragm is not seated correctly in its notch. Take the intake elbow off and check that the piston in the carb correctly aligns within the tunnel. A mistake I once made with nearly the same symptom.

    /Guenther
    2017 F700GS

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