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Thread: 1984 R80RT idling issues

  1. #1

    1984 R80RT idling issues

    My R80RT rode great when I left my native Milwaukee. The carbs were synced and it purred. Since then it has started idling very unreliably while in city traffic. It is now very difficult to start and constantly wants to die if I don't hold throttle on constantly while at stop lights. I'm now in Burlington, VT and currently riding across the country for the summer. It rides decent on high speed roadways, but doesn't quite seem to have the acceleration it had 1800 miles ago. Going up some of the hills in the Adirondacks I would lose speed.

    Is this an elevation issue? Will I need to constantly adjust my mixture screws throughout the entire trip? Does this indicate too rich or too lean?

    Any ideas?

  2. #2
    Liaison 20774's Avatar
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    When's the last time you checked the valve clearances, especially the exhaust? Sounds like you might have lost all the clearance. Also, check the timing.

    Kurt in S.A.

  3. #3
    Loose Cannon flash412's Avatar
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    The FIRST thing you need to do is replace the spark plug caps with NGK 5k caps. The OEM ones are total crap, especially if they are 20 years old.
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  4. #4
    The guys at Motorwest in Milwaukee said the valve clearances were good. The ignition is electronic.

  5. #5
    Liaison 20774's Avatar
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    Quote Originally Posted by eddiekilowatt
    The guys at Motorwest in Milwaukee said the valve clearances were good. The ignition is electronic.
    How long ago/miles were the clearances checked? The reason that I ask is that the '81-'84 models, especially the 1000cc models, were prone to valve face plastic deformation due to improper metallurgy in the valve seats. Not so much the 800cc bikes, but still they had the same bad seats. If it's only been 1000 miles or so, then it's probably not the valve clearances. But the clearances have been known to close up rapidly followed closely by the engine swallowing a valve. I'm not saying that's happening here, but if it were me, I'd want to know it wasn't the problem so I could look somewhere else.

    I get the impression that you don't set the valves yourself. Even if you didn't do the valves yourself, it's still "easy" to see if you have clearance or not. On a cold engine, take off the valve covers and the plug covering the hole to the timing marks. Put the bike in gear, say 3rd or 4th, and rotate by hand the rear wheel. Watch or have someone watch until you get the flywheel mark at TDC in the hole. Then check the pushrod tubes on one side or the other. One side will be tight, one side will be (or should be) loose. You can spin the pushrod tubes in your fingers. If they both spin, then rotate the rear wheel so that the engine/flywheel rotates exactly one revolution to the TDC mark again. Now the other side should have loose pushrod tubes. If you can spin all four pushrod tubes easily, then you probably have OK clearance. You could also push on the ends of the rockers and visualize the clearance. The exhaust clearance should be nearly double the intake clearance.

    If it's not valves, then possibly the diaphragm in the carbs has gotten a hole in them.

    What about the battery and your charging system? What kind of voltage do you read across the battery with a separate meter? At 4K RPM, it should be on the order to 13.5-14.0volts. A bad battery can also cause poor running conditions.

    There are resistance checks from one spark plug cap all the way over to the other spark plug cap...should be about 22K ohms. If your caps (as mentioned earlier), wires, or coils are breaking down, you could be getting a weak spark.

    Kurt in S.A.

  6. #6

    update

    I pulled the plugs and the left was black and sooty. The right had the usual tan/grey color. Checked the pilot jets in the carbs and both were clean.

  7. #7
    The battery is new and works great, charges fine. It never drops below 12 while riding, charges well when on the roadway. The valve clearances were checked before I left-about 2000 miles ago.

  8. #8
    Liaison 20774's Avatar
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    Quote Originally Posted by eddiekilowatt
    I pulled the plugs and the left was black and sooty. The right had the usual tan/grey color. Checked the pilot jets in the carbs and both were clean.
    Well, looks like you found something. Still could be the diaphragm at the top of the carb. I wonder if the jet stack is not put in correctly?

    Try checking the level of fuel in the float bowl. Turn on the gas for a few seconds, then turn the petcocks off. Carefully, and as quickly as you can, take the float bowl off of each carb. The height of the gas in each the center of each bowl should be in the neighborhood of 20-22mm. You might find that the left carb height is higher than that...that would result in running rich, and black sooty plugs.

    You might want to let some gas flow out of the left carb onto the ground...just a bit. Maybe you have a piece of crud that's not letting the float shutoff. Check to be sure that the float shuts off at the proper level. With the petcock turned off and the carb bowl off, hold the float up with your finger and turn on the petcock so that no gas is coming out. Slowly lower the float until gas starts to flow than raise the float to the point where the gas flow stops. There's a mold line on the float that should be parallel to the lower edge of the carb body. If it's not, then you need to carefully bend the small tab to reset it. It might be possible to bend the tab with everything in place if you're careful. If not, then the pin holding the float in place has to be removed. The pin is knurled on one end and it should only be moved in one direction...I think that you should go to the opposite side of the knurled section and push the pin out. Be careful not to hammer/pound etc. such that you break off the ears on the float tower. That'll ruin your day...

    Sounds like it's a fuel issue. Good...something a little easy to troubleshoot. Check the fuel level first before deciding to check out the diaphragm. You might be able to watch the diaphragms work by taking the air intakes off and starting the bike. While reving the bike, see if the slides move about the same when looking in the rear side of the carb throat. If the left doesn't go up as high, it could be running rich and/or have a problem with the diaphragm...or the slide is sticking.

    Kurt in S.A.

  9. #9
    This is the constant depression Bing Carbureter. I think you're referring to the older slide version. I do see what you mean, though...

  10. #10
    Liaison 20774's Avatar
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    Quote Originally Posted by eddiekilowatt
    This is the constant depression Bing Carbureter. I think you're referring to the older slide version. I do see what you mean, though...
    The Bings (CV for constant velocity or constant depression, too) also have a slide. In these the slide is not directly connected to the throttle cable...the cable is connected to the butterfly in the throat of the carb. You twist the throttle and open and close the butterfly. As air flows through the throat of the carb, a passageway creates a vacuum above the slide and pulls it up. Let off the throttle (ie, close the butterly), and the in-rushing air slows and the slide drops. In the early Bings or Del Ortos, the throttle cable was connected directly to the slide and you yanked on the slide via the grip.

    Kurt in S.A.

  11. #11
    Dang Kurt. You know your stuff. Feel like taking a trip to Vermont? ha ha ha

  12. #12
    Liaison 20774's Avatar
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    Quote Originally Posted by eddiekilowatt
    Dang Kurt. You know your stuff. Feel like taking a trip to Vermont? ha ha ha
    Well, I did stay at a Holiday Inn Express last night! Seriously, you fiddle around enough and read enough posts, you begin to catch on after a while. I'm sure there are MOA members somewhere nearby who could lend a hand...got your Anonymous with you? Good time for the Anonymous to be on-line. Hey, wait around for a month and a whole bunch of them will be up there for the National!!

    Kurt in S.A.

  13. #13
    Actually, the Anonymous is meeting me in New York, it's getting sent to the venue I have a reading at. As of Tuesday hopefully I'll be able to check it out, I've never had my eyes on one. This is my first BMW, it's only been underneath me about 2 months.

  14. #14
    Liaison 20774's Avatar
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    I'm not sure I catch all of that, but I can understand being a bit bewildered having the bike only a couple of months. If you think you need assistance, at least to check out whether it's easily fixable or it needs more attention, I'm sure we could find someone to help out. I've got my Anonymous book and knowing what cities you're closest to, I could find some phone numbers for you to call. Let me know, and I'll send you a private message...apparently there's a feature at the top of the screen that allows that.

    Kurt in S.A.

  15. #15

    Just an update

    It DID end up being the exhaust valves, they had gotten to be too tight.

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