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Thread: R60/6 high speed miss

  1. #1
    Amanaland
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    Question R60/6 high speed miss

    I have owned a 1975 R60/6 since 1976 and it has a high speed miss that is becoming progressively annoying. I really haven't ridden it much in the past 25 years but periodically try to tweak something else to see if I can get it in better tune. In the last year its had points and condenser as well as new Bosch coils.

    For what its worth, after installing the new points, I wasn't able to retard the timing to the point that the "S" showed up in the timing window at idle. The symptom that I'm dealing with is a miss at about 5500 RPM, it starts and idles nicely. Do the springs on the mechanical advance get weak? and not fully retract the weights at idle? Would this cause my high speed miss? (the timing mark moves when I rev the engine)

    I have had the carbs apart and synchronized them to the best of my ability, using the BMW shop manual. Maybe that's the problem too - I'm at a loss...

    Another on-line message board suggested that I had a vacuum leak, "check for missing hoses or a leak at the intake manifold". My carbs are the very simple Bing side draft - not the vacuum ones and they connect directly to the head. No hoses there for sure.

    Another suggested that it might be plug wires. Many years ago I replaced the original wires with aftermarket GM wires. I need to pull the tank and check resistance still.

    Every time I think about taking it into the shop, I pucker right up. Is there anyone out there with suggestions for an old guy with the mechanical aptitude of a third grader? The bike is very clean, 33,000 miles but this miss seems to be getting worse. Top speed is down to about 80 now.

    help

  2. #2
    P Monk
    Join Date
    May 2005
    Location
    Orange, Texas
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    847

    Omega ignition

    I wanted to keep the points on my 74 but had the same problem you describe. I could get timing right at idle but was too advanced at speed.
    Finally installed the Omega and set idle (slightly advanced by accident).
    I went from 4 to 3 on adjustable advance curves to get the timing slightly retarded at 3k+ to help with pinging.

    Someday soon I am going to have to pull the heads and decarbon.

    With the omega the ghost timing marks are gone. I have run up to redline (in 4th)
    with no miss and starting and idle are both improved.

    Plus If I want to run on the points all I have to do is switch two wires and pull the green wire to the omega and I am back on points.
    P. Monk
    74 R90/6 (the Black Hole), 2011 R1200RT.

  3. #3
    Liaison 20774's Avatar
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    Quote Originally Posted by Amanaland View Post
    For what its worth, after installing the new points, I wasn't able to retard the timing to the point that the "S" showed up in the timing window at idle.
    I understand this problem to be that the points gap is not right. The gap really isn't that critical but it does have to be a gap. Gap too wide, the points never close; gap too close, the points never open. Somewhere in the middle is just fine. On a 2-cylinder engine, the gap (aka dwell) is not as important as it is on say an 8-cylinder engine. As long as the gap is sufficient to allow the coils to saturate, you're in good shape.

    What about any corrosion on the spark plug towers on the coils? What's the reistance when reading from one plug cap all the way over the other other plug cap? You're not running excessive resistance in the ignition wires are you? For a points bike like yours, the caps should probably be 1K ohm.

    You could consider running a Dyna ignition booster which keeps the voltages down across the points but provides solid current to the coils.

    How's the valve clearances?
    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. #4
    Amanaland
    Guest
    Thanks for the ideas. Its been a long time since I set the valves, and couldn't find what the correct resistance on the plug wires should be. The coils are about one month old, new Bosch 6 volt so I don't think that corrosion would be the problem.

    I see an EBay supplier for plug wires wanted to know which resistance you would want when ordering, 1K or 5K. I assume I would need the lower resistance?

    I'll set the valves, re-check the point gap and check the wires for too much resistance.

  5. #5
    Liaison 20774's Avatar
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    For your model, the total resistance should be around 12K ohms IIRC. That works out to be 5K for each coil and about 1K for each cap. If you had the later /7 ignition system and the later models with the electronic ignition, that would be an additional 8-10K ohms (20-22K total) because of the 5K ohm spark plug caps.

    What kind plug caps are you using? A lot of people here like the NGK caps.

    Seems like Matt Parkhouse had an article in the MOA News on this lately...
    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. #6
    #4869 DennisDarrow's Avatar
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    First of all.........WELCOME ABOARD

    Earlier it was mentioned about point gap and advance springs. I might add, to check out the condensor and replace that while you are checking what has been done. The point gap IS important, because this gives you timing "room" as you rotate the point plate to get the timing set properly.
    Yes, advance springs "wear" out; but are readily available. I suggest checking out and calling, http://benchmarkworks.com/. Also, there is a specialty grease available for the points that you put on the points cam/felt and another specialty grease for the advance mechanism itself.
    While you have the advance off, do make sure to check that the cam itself is clean and smooth. An irregularity here could cause or set up a "bounce" vibration that would amplify at high RPM and cause a miss.

    BE SO CAREFUL TIGHTENING THAT NUT THAT HOLDS THE ADVANCE MECHANISM. It strips the threads off of the bolt, which is actually the end of the cam so very easily. Just tighten it. NOT so called TORQUE it. I use a 10mm wrench that is quite short and use the leverage available in my fingertips..........

    Anyway........Good luck.........Dennis
    Last edited by DennisDarrow; 05-19-2009 at 10:49 AM. Reason: speliing/text

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