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Thread: no idle left side

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  1. #1
    beemerfield
    Join Date
    Apr 2006
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    233

    no idle left side

    I have tried 3 sets of carbs and several different people have tried to tune the 1971 R75/5 with little success.

    I installed later model carbs last week which seem to help a little. The bike is rideable and seems to run ok at any speed above idle. However, when I try and balance at idle using the grounding method, the left side dies. If I rev any, the cylinder kicks in at any speed above idle. It is the left side only and right side idles well.

    I cleaned and blew air through the carb, checked cables, choke off,diaphram appears OK,new plug, new boots from carb to cylinder, switched sides with coil/plug wires. Took cover off to look at points and it appears they are ok, but not sure how to tell if they are not (they are new). If the shaft is bent, how can you tell?

    Also- just curious- the cover says "Hilderbrand" on the front and inside has a BMW logo, below which is a little "clock face" with 70 in it ad 11 to the rigt of that. It has a part # 1.255.0059 which does not match the parts list. Does anyone know anything about this cover?

    Thanks for any ideas/info!
    beemerfield

  2. #2
    Registered User
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    Jun 2003
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    Northern Front Range, CO
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    a bent shaft will show as a wobble in the points assembly, and as a doubled S or OT mark when using a timing light to check the timing.

    kind of a "dumb" question- but you have attempted to adjust the individual carb's idle speed, yes? (i would tend to think so, especially having gone thru 3 sets of carbs)
    Ride Safe, Ride Lots

  3. #3
    James.A
    Guest
    Roger, If you haven't already done this, it might behoove you run a compression check on both cylinders to make sure they are within about 10% of each other.

    On my recently resurrected /7, I had a devil of a time getting the carbs to balance until I discovered a significant divergence of compression from one side to the other.
    It's the kind of thing you don't want to find, but you have to know for sure that your'e good on that parameter.

    This /7 would attain a good highway speed, but couldn't get the carbs to work together lower speeds. Compression was 120lb on one side but only 90lb on the other.

  4. #4
    Registered User
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    May 2012
    Location
    VA
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    248
    I expect the spark is ok, since the shorting (grounding) method for the plugs is used. I would see if the engine speed can be changed with idle mixture adjustments, then use a timing light to check the timing, then check the valve clearances, then check the compression on the cylinders. Turning the idle adjustment screw in (far) enough will bypass the idle circuit - although for the CV Bing's the idle adjustment extends into the partial throttle position. Good luck!
    Stan

    AH# 13238

  5. #5
    beemerfield
    Join Date
    Apr 2006
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    233
    I've checked the compression and they were at about 145-155. I set the valves, but as that has been some time ago, I guess I could double- check them. I have not used the timing light. I have adjusted the idle speed, but did not want the main valve to "override" the idle speed circuit. I could try and mess with it some, but am not really comfortable with adjusting yet. That is why I have had others try.
    beemerfield

  6. #6
    beemerfield
    Join Date
    Apr 2006
    Posts
    233
    If it is a bent shaft, is it a major issue? What is the repair/ junking the bike process?
    beemerfield

  7. #7
    beemerfield
    Join Date
    Apr 2006
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    233
    OK- finally an update- I replaced the springs on the advance unit, re-set points, re-checked valves and found no change. Using the "shorting out" method, the left side just quits at idle.

    Next to re-check compression, check the tube between carb and cylinder to see if it is tight and then swap carbs side- to side.

    I also put some Seafoam in gas and bought new 93 octane.
    beemerfield

  8. #8
    beemerfield
    Join Date
    Apr 2006
    Posts
    233
    Latest update in case anyone wonders- I finally was able to adjust my front brakes so they are decent now which makes a big difference in riding!

    It was so nice, I decided to quit medding with the stupid idle and just ride. Went for longest ride since I got it going again and it didn't break or catch fire! Nice 70 mile ride. Still won't idle correctly on left carb, but runs fine at any rpm above about 1500.

    Hoosier Beemer Rally is this weekend, so hope to do more riding/tuning there.

    Thanks for reading!
    beemerfield

  9. #9
    Registered User
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    Jun 2003
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    Northern Front Range, CO
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    roger- any chance that the choke assembly is installed backwards on that left side carb?
    Ride Safe, Ride Lots

  10. #10
    beemerfield
    Join Date
    Apr 2006
    Posts
    233
    I will look at choke assy. However, since I have had this problem with 3 different carbs, I keep thinking it is something else. Looks like rain for at least the first of the weekend, but maybe Saturday afternoon I can mess with it.
    beemerfield

  11. #11
    beemerfield
    Join Date
    Apr 2006
    Posts
    233
    FINALLY! Thanks Don- carbs are balanced and seem to be working properly.
    Needed someone who has experience to notice that both idle and speed screws were both too low and so now it is a matter of riding and hoping the plug dosen't foul.

    Thanks to everyone that has helped on getting this bike back from the dead. It has been a real group effort, so now when you see it at a rally, you should feel good knowing you have been a part of it!

    I'm planning on taking it to Falling Leaf and just RIDING it!
    beemerfield

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