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Thread: Setting timing on '76 R90/6

  1. #1
    Bill the Cat geisterfahrer's Avatar
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    Setting timing on '76 R90/6

    I was working on my new old bike this evening, trying to sort out a hard start issue, when I discovered that at even at maximum retard on the ignition plate, the timing was still at full advance at idle.

    I used a Dremel to elongate the holes in the ignition plate, and was able to get the idle timing set to the "S" mark.

    Now the bike starts easily, and pulls like a tractor.

    My question is, is this a common problem? I have no idea what brand of points/condenser was put on this bike by the PO, so are there aftermarket points that will cause this condition? If I put in a set of genuine BMW points, will I be able to set the plate back to a more "normal" position?

    TIA,

    Kevin

  2. #2
    RecycledRS
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    The advance mech. is stuck in full advance. Remove the bean can and lubricate the wieghts.

  3. #3
    Bill the Cat geisterfahrer's Avatar
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    Not a bean can ignition on this machine. This one has the old-school points and condenser system. And, I have checked to make sure the advance does work correctly (it does).

  4. #4
    Nutfarm
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    No bean can on a 76, but it does sound like the advance is stuck.

    Ken G.

  5. #5
    RecycledRS
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    Oooops, didn't know they didn't have a bean can. If the advance is working are the springs strong enough to resist it going full advance before it should?

  6. #6
    Bill the Cat geisterfahrer's Avatar
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    I have tested the advance using a Tiny Tach (the cluster tach is busted) and a timing light, and it seems to be working well within spec.

    I haven't worked with a points/condenser + mechanical advance ignition system since my '73 Beetle, so I'm definitely a little rusty when it comes to diagnosing problems. I'm just wondering whether a set of aftermarket points can cause the timing to be so far advanced, and why?

  7. #7
    #4869 DennisDarrow's Avatar
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    Have you checked your points gap to be positive it is set correctly? Go ahead and get some "real" points. Is the points cam clean? Did you try setting the points using a static method?

    Just thoughts.......Dennis

  8. #8
    Bill the Cat geisterfahrer's Avatar
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    Dennis,

    I have checked the point gap several times. I had to reset them each time I took the timing plate off to elongate the slots. I have the original BMW toolkit feeler gauge, and I am a toolmaker by trade, so I am pretty comfortable with the gap setting. The cam is clean, and has no visible wear on the bearing surfaces. I set the initial timing using the static method, and then fine-tuned it with a strobe timing light.

    I will go ahead and get a set of "real" BMW points, and see if they make any difference.

    In the meantime, I'm going to put some miles on the bike as is, and see how she feels. The difference between the way she runs now and how she ran when I picked her up is astounding. If I had the traction, I could probably pull a triple-gang plow with her now

  9. #9
    Administrator 20774's Avatar
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    You initial problem was that the points gap was not correct. It may have been correct based upon your measurements, but the gap and the rotation of the plate need to be played against each other. There should be no reason to elongate those holes in the points plate. A small change in gap results in big changes in the firing point.

    In the big picture, there just needs to be a gap. The time period of no points gap during the rotation of the camshaft is the saturation period for the coil. When the points open, the coils create the spark. If no gapping, no spark; if there's gap all the time, no saturation. The exact amount of gap is not so critical on a 2-cylinder engine...more important though on those old V-8 motors.

    So, I think the right thing to do would have been to widen the gap a skoosh. A wider gap means the points begin to open sooner during the rotation. That would have resulted in the ignition firing just a bit sooner, eliminating the retarded condition you first found.
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  10. #10
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    point gap

    Kevin: Notwithstanding all the advice already given, I had the same problem with a 77 /7. No matter what I did, I couldn't get the points properly set without lengthening the adjustment hole on the plate. A few passes with a round file and I was able to get the right timing and gap. When I finally did get another plate and compared the holes, the newer plate did have a longer one by a few mm. For what it's worth.

  11. #11
    No bugs in winter OHScot's Avatar
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    Check the slack in your timing chain. Rotate engine one direction till the cam moves, rotate it back till cam moves and measure the degrees of play. May have jumped time a little or have too much slack. Better to check now than later.
    "Wow I didn't know BMW made motorcycles, Yeah I think Honda does too."

  12. #12
    Scraper JohnW67's Avatar
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    Purchasing Points

    Note that if you're purchasing new points, many are now made in China even though they are BMW parts. The rubbing block is too high on the one's available from most suppliers. I understand that Ted Porter's Beemer Shop is buying from a german supplier and the block is at the correct height.

    Check here: http://www.beemershop.com/

  13. #13
    Bill the Cat geisterfahrer's Avatar
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    I just ordered a point/condenser set from Max BMW. I hope they are good parts. Does anyone have the specs on the height of the rubbing block?

  14. #14
    Rally Rat
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    There is quite a bit of slop in the index for the advance mechanism on many bikes. Retarding the advance mechanism's location frequently will allow the timing to be corrected without filing the points backing plate.

    It's also worth rechecking the points gap after moving the plate. Apparently (I've never checked this) the pates are not truly round.

    However, it's also acceptable to open the slots a bit, as long as the points don't interfere with the wire bracket on the bottom screw.

  15. #15
    Airhead krehmkej's Avatar
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    Setting the gap on these is a bitch at best as the ATU is in the way.

    Northwood Airheads makes a little tool that makes the job much easier:

    http://www.northwoodsairheads.com/Tools.html

    Once you are certain the gap's OK you can go from there.

    My $0.03, YMMV.
    -jwk-

    1978 R80/7

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