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Thread: New Member Question and Intro 1975 R90/6

  1. #31
    Airhead
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    Consider lighter throttle return springs on the carbs

    Now that you have the throttle working properly, consider installing lighter throttle return springs on the carbs. These are the external springs visible on the engine side of the carb's body.

    The stock springs are stiff, meaning you will be fighting them on long trips (the throttle 'lock' screw can help, but is a sub-optimal solution, IMO). The results is stiff neck muscles.

    I installed a pair of EZ Pull springs on my 1975 R90/6 years ago and have never looked back.

    Left Bing carb #: 64/32/11; right 64/32/12.

    You want the Type 908 for your machine.

    Needle nose pliers can help with the job.

  2. #32
    Registered User bandersnatch's Avatar
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    Hi Folks,

    Being in the middle of preparations for my wife's 60th birthday party this weekend has kept me from any serious time with the R90/6. I was able to replace the headlight bulb so I now have a low beam AND a high beam. One more step toward a ride-able bike.

    Looking over the wiring diagrams I cannot for the life of me figure out what this wire is. There doesn't seem to be anything left over going to the back of the bike and it has been there since I got the bike so it doesn't seem to be critical to the bike running and starting. Any suggestions on what this might go to?IMG_0154.jpg

    Note - the white paper is just to highlight the wire as a black wire against a black frame is difficult to pick out.
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

  3. #33
    Liaison 20774's Avatar
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    Does the other end of the wire disappear into the wiring harness or has it been added later and it just following the wire run? Any chance to see where the other end is?

    Since it has the length to end where the coils are, almost seems that's the region where it might go. For the stock coil setup, a green/black wire comes into one coil connector (typically the left one), then there's a small black wire jumper over the other right coil, then a black wire coming off the outside connector on the right coil which goes to the capacitor under the front engine cover. Do you have all those?
    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!

  4. #34
    Rally Rat 1074's Avatar
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    Black wire

    I've known about that wire since the 70s and still don't know where it goes and what the function is. Don't worry about it.
    Boxerbruce

  5. #35
    Liaison 20774's Avatar
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    It could be the wire that eventually attached to the coil for the electronic tach in 1978. Prior to that happening, BMW began to make a compatible harness for that eventual change and put those harnesses on earlier models. All functions still worked but a few connection points went unused. '75 models seem a bit early but you never know.
    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!

  6. #36
    Registered User bandersnatch's Avatar
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    Just as you say, it disappears into the wiring harness. The other three wires (green/black, black jumper and black to capacitor) are all there.

    Good to know it has puzzled others and I can safely ignore it.

    Thanks all!

    Quote Originally Posted by 20774 View Post
    Does the other end of the wire disappear into the wiring harness or has it been added later and it just following the wire run? Any chance to see where the other end is?

    Since it has the length to end where the coils are, almost seems that's the region where it might go. For the stock coil setup, a green/black wire comes into one coil connector (typically the left one), then there's a small black wire jumper over the other right coil, then a black wire coming off the outside connector on the right coil which goes to the capacitor under the front engine cover. Do you have all those?
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

  7. #37
    Registered User bandersnatch's Avatar
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    Got to spend a few minutes in the garage today and measured the voltage at the battery. Nominal voltage was around 12.4V with absolutely no change when I hit the starter button.

    I skipped the check of the coils in favor of trying an idea I saw on another post of shorting the positive terminal to the solenoid wire. Did a happy dance when the bike fired right up and ran well!

    So apparently, the starter, points and coils are fine and I get to track down whatever else is causing the starter switch to not work.
    I'm leaning toward Kurt's diagnosis of a bad starter relay since that seems to be where the issue started. Any thoughts on the $10 relay from Motorrad Elektrik? It looks identical to the stock one which I'm seeing anywhere from $37 to $75. I'll readily throw a sawbuck at the problem - if that's not the issue, no big loss and I have a spare on hand.

    Or should I play it safe and order an OEM or OEM replacement relay?

    Thanks,
    Larry
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

  8. #38
    Rally Rat 1074's Avatar
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    Motorrad Electric

    Get the part from Motorrad Electrik! This is the way to go! When I had my independent airhead shop I did a lot of business with Rick.
    A case in point involved an alternator rotor from him that only lasted one day. In the course of our followup conversation, Rick asked me what my hourly rate was. So the next day I got the replacement part with a check for an hour of labor!
    This man is my hero.
    Boxerbruce

  9. #39
    Registered User bandersnatch's Avatar
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    Bruce, thanks for the recommendation for Rick at Motorrad Elektrik. I spoke with him and ordered several items that I know I'll need.

    Next question for you more experienced Airhead tinkerers. I would like to keep the bike as stock as possible, including the rear shocks. I understand OEM shocks are no longer available but have an opportunity to buy a pair of like new shocks that were taken off a 1979 R65 shortly after purchase.

    The seller claims that they will fit most 750, 900 and 1000cc bikes, true or not?

    The shocks do not have the covers like the ones on my R90/6, can I transfer them to these shocks?

    Thanks all,
    Larry
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

  10. #40
    Liaison 20774's Avatar
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    I don't think the R65 shocks will work.

    1) Different part numbers for R90/6 and R65 per RealOEM

    2) Ikon's website has a different shock part number for the two bikes.

    Ikon does have an offering 7610-1298 with /6 shock covers for $500.
    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!

  11. #41
    Registered User bandersnatch's Avatar
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    Thanks Kurt. I saw the same thing as you, that Ikon shows different part numbers. Possibly different size posts, distance between the eyes or load capacity.

    Too bad, the used shocks were very reasonably priced.

    I may go ahead and ask the seller why he thinks they will fit earlier airheads, I'll keep you posted on his response if I get one.

    Regards,
    Larry
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

  12. #42
    Liaison 20774's Avatar
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    The LWB models had shocks that were around 335mm eye-to-eye or 13.2 inches. The R65 shocks are about 0.5 inches shorter. Using a shorter shock is going to do some nasties to the handling of the bike.
    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!

  13. #43
    Quote Originally Posted by 20774 View Post
    The LWB models had shocks that were around 335mm eye-to-eye or 13.2 inches. The R65 shocks are about 0.5 inches shorter. Using a shorter shock is going to do some nasties to the handling of the bike.
    Unless you also lower the front which is usually quite easy to do.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  14. #44
    Registered User bandersnatch's Avatar
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    That's a very good reason not to purchase/install the R65 shocks and exactly the information I was hoping to get.

    While lowering the front would be possible, I'd like to experience the bike as it would have been straight from the BMW factory, exactly like I'm doing with my MGA.

    Thanks so much, I love this forum!

    Larry

    Quote Originally Posted by 20774 View Post
    The LWB models had shocks that were around 335mm eye-to-eye or 13.2 inches. The R65 shocks are about 0.5 inches shorter. Using a shorter shock is going to do some nasties to the handling of the bike.
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

  15. #45
    Registered User bandersnatch's Avatar
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    Progress!

    Puttered with the bike tonight, I think I found the problem with starting. Actually, two problems - the starter relay seems to have decided it was tired of life and checked out plus the ignition (points) seems to have somehow gotten stuck open. I pulled the mechanical advance off and played with the points and when I put it back on I suddenly had spark again. Possibly due to the advance rotating on the shaft so I'm going to try my trick of filing a flat on the opposite side of the camshaft to lock it down.

    I started it by jumpering across the solenoid with a remote starter switch. Fired right up - insert big grin here! Put on a helmet, rolled it off the kickstand and drove under its own power for likely the first time in over 20 years. She has at least 25 year old tires, no front brake and no instrument lights, but darned if she didn't take me all the way around the block!

    On the schedule - new tires, new spokes, fix the dash and brake lights, get the neutral switch working (before the starter relay died I had to hold the clutch lever in to start it), rebuild or replace the master cylinder and brake calipers/pads and install the new starter relay.

    It was a good day!

    Larry
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

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