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Thread: 1976 R75/6 looses power?

  1. #1
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    1976 R75/6 looses power?

    I have a new to me 76 R75/6 I have owned for about a month. I have been working out bugs snce I got it, the bike sat for about 1 year after it was supposed to be gone thru by BMW servce center. Recently when I start it in the morning it does not seem to have any power until it get good and hot. Yesterday on the highway it did not seem to have any power at around 70 mph. It actually would seem to loose power when I tried to open it up and it did back fire as it boged down, I could barley keep up with traific on steep inclines at 65-70 MPH. I tried to open it up to see if it would accelerate and it just could not go faster than about 70. It feels kinda like it is only running on 1 cylinder.
    How can I tell if this is a fuel issue, a compression issue or a spark issue. This is my second BMW and my first classic air head but so far this bike has been a great disappointment. The bike is in great condition and looks very nice but so far I have had to work on it every week t try and work out the bugs especially with the carbs. The service center did help get the carb issues worked out, at least I think so. I am not sure they are right still. Appreciate any help I can get. thanks randy

  2. #2
    Administrator 20774's Avatar
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    Usually lack of power at cruising speeds over 60 comes down to a torn diaphragm in the carbs. You didn't say if the carbs were overhauled but this might be something to check.

    Also, you might want to be sure that your floats are set correctly. If the floats are set too lean (they shut off fuel flow too quickly), then you could run out of fuel in the bowls at speed. It doesn't explain the problem at when starting cold.

    Backfiring also suggests timing, probably too retarded.

    Just some things to check...
    Kurt -- Forum Administrator ---> 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!

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    R75/6

    Thank you for the response. I also looked at the 2 mufflers, the right looks normal with some black corbon on it but the left has almost no carbon on it other than in the very center cone, none around the larger part of the opening. I pulled both plugs and the left is deffinately different, it has build up on the electrode and in the plug, almost looks like rust the way it is built up on it. It has build up that is milk chocolate colored and there is a fair amount on it. I get good spark to both, compression seems ok. I am thinking the timing is off and I still suspect the carbs are not right. I appreciate any advice I can get. I will get this worked out and then it will be a sweet ride. thanks randy

  4. #4
    Administrator 20774's Avatar
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    If the timing is off, it would affect both cylinders the same...that probably doesn't explain the plug difference. You might check for corrosion in the central plug on the ignition coils. You might not be getting the hottest spark if corrosion has built up in where the spark plug wire goes into.
    Kurt -- Forum Administrator ---> 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!

  5. #5
    #4869 DennisDarrow's Avatar
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    "BMW Service Center" sounds like a car wash/tire change place.........Anytime you get a "new" bike/car/anything, YOU need to go through it with a major tune-up/service.......Yes:

    all the fluids
    Valve Adjust
    points/condensor
    timing
    carb cleaning
    carb rubber parts..... Kurt is right,THIS IS WHERE YOUR LACK OF POWER
    IS....torn diaghram
    Carb Sync

    Grease clutch, throttle, swing arm, brake lever

    The plug that is chocolate colored is what you want. Not a lot of build up of crud but that color. You do NOT want the muffler to have carbon or black; but clean or a light grey...........

    If you don't know how to do this or are not willing to LEARN HOW, find someone local who will.........if you are gonna get into this machine for awhile...LEARN HOW

    Your information doesnt say where you are but I betcha that someone is close to help you.........God bless........Dennis

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    R75/6

    Thanks guys, I am willing to learn and normally have done all the maintenance on my bikes so I am faily capable. The left plug has a milk chocolate build up that is very thick and irregular, just like rust would be but it is not rust. The bke has electroninc ignition but I am not sure which brand yet, I will have to find out and then find out about the settings for that unit. The carbs were supposed to have recently been rebuilt but I
    will open them up and probably have to rebuild them both and make sure the floats are set right. Probably also a good time to check valve settings. I am in Northern KY just south of Cincinnati. thanks, randy

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