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Thread: no idle left side

  1. #1
    beemerfield
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    Apr 2006
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    239

    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
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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
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    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
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    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
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    If it is a bent shaft, is it a major issue? What is the repair/ junking the bike process?
    beemerfield

  7. #7
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    A bent shaft will show up in the points advance assembly as a wobble, or as double timing marks when using a timing light. It's pretty obvious if the advance unit wobbles with the timing cover off. The double marks when using a timing light is an indicator also, but not as obvious as simply looking at the timing advance unit.

    Quite honestly, I think your original carburetor idle circuit is clogged/dirty. I am not sure where the idea of swapping carburetors came from but, unless you have another R75/5 for parts, getting good results is unlikely. The idle jets are sized for the carburetor and engine. I think your best solution is to clean or partially rebuild the original (correct) carburetor. Good luck!
    Last edited by Stan_R80/7; 08-27-2012 at 04:44 PM. Reason: grammar
    Stan

    AH# 13238

  8. #8
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    A couple questions

    Did you have the carbs off or the throttle slide in the full open position when you did the compression check?

    Was the motor at operating temperature when you did the compression check?

    Did you have both spark plugs out when you did your compression check?

    When you clean out your carb and jets its important to make sure that you get all the build up and gunk out of the passages and the jets especially the jets in the idle circuit. Those jet orifices can be open to let fluid through but still have enough blockage to distort and weaken the spray pattern which would affect the idle.

    Another possibility is a cracked or loose valve seat or head casting that may only affect the motor when its hot.

    Have you checked the condition of the coils and condenser as either one can throw things out of whack at any speed but not others.

  9. #9
    beemerfield
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    Thanks, Stan. I looked at the points assembly last night and don't really see a wobble, but my eyes are not that great and I would think a wobble would have to be very pronounced for me to note.

    This bike is a long story that should have been documented in it's own "rescue" story, but I have been taking calsses/working over the past 5 years while i have been trying to get this thing going. i now have a little more time to work on it.

    I tried the carbs that came with the bike (it was heat damaged in a fire- melting plastic and blistering paint, but all else seems workable including original wiring). I rebuilt the carbs and as they are on Snowbums' list of trouble carbs, sent them back to Bing for new seats and hadthe fittings installed for my Twinmax. No one could seem to get them running right, so I put on another set that i bought at a swap meet "from a running bike". They have the same early "difficult" serial numbers as the origininals and again, did not work right. However, they haven't been cleaned or anything (but look ok).

    I bought a pair of later model Bings last week and found they have the alcohol resistant float kit installed (which also caused me some concern). I put these carbs on and it seems to run better than before. Just trying to balance them now has led me to this issue. I took the left one apart, cleaned it and blew air through it. I put a brand new idle adjustment screw and o ring in from the original carb. None of this seems to do anything.

    See- long story! i have had the bike about 6 years now and this is the first summer I have ridden it. It will need new pushrod seals also, but I will wait for a while to do that.

    Thanks for reading my post!
    beemerfield

  10. #10
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    Ok, having more than one of the (correct part number) carburetor's makes sense. FWIW, I had a similar situation upon reviving my R80/7. Eventually, I realized the idle circuit was not working but the bike would run. The problem was with the right carburetor instead of the left. The right cylinder would not idle when using the grounding technique, regardless of the idle mixture adjustment or the choke setting.

    I had some Berryman's Chem-Dip (the modern version) from other carburetor work and cleaned the right carb body by dipping in the cleaner. The floats, bowl, diaphragm & top, and piston were removed then the body was put in the Chem-dip basket for about 4 hours. Afterward the idle mixture o-ring was replaced with the main jet o-ring. The carburetor top control cables were not removed or adjusted so reassembly was just putting the floats, bowl, piston w/diaphragm back with the top. The Chem-dip worked pretty well and the modern version does not eat up o-rings.

    I have the alcohol floats and plastic bowls. They seem to be holding up OK after 20+ years. Although, I needed to clean the float guides using some pipe cleaners and Brasso to stop the floats from sticking.

    Depending on the environmental laws and the state you live in, a cleaner such as Chem-Dip may not be available. Some members have used pine-sol and water. I did not find the spray cleaners (i.e. Gumout or compressed air) reached the idle circuit in the body. Only soaking in a solvent cleaned the idle path.

    Maybe it is not a clogged idle circuit and is something else, but it sure doesn't sound like it based on your description of the symptoms and engine condition. If I were you, cleaning the left carburetor body would be my next step. Good luck!
    Stan

    AH# 13238

  11. #11
    Registered User ebeeby's Avatar
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    A tight exhaust valve would leak compression and kill the idle.

  12. #12
    beemerfield
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    OK- now I feel stupid. Tonight, I triple checked the vlaves. (Hint to anyone reviving a bike-keep a journal of all you do and when you do it.) Intake was just a little loose. I then removed left float bowl, cleaned the jet in the bowl, the idle adjustment screw was removed/cleaned and I pulled the idle jet/cleaned and installed a new idle jet o ring. Then I went for a ride, felt it was running a little worse. Set up the timing light and noted I could not tell what was happening because the marks seemed to be jumping around. Then I knew it must be timing related. I had the front cover off as I had been watching the points to see if they were wobbling. I then decided to triple check the points gap.

    At that time I noticed one of the springs on the advance unit was missing!

    I have looked at this thing so many times I couldn't count. My eyes really have gotten bad.

    So if this is not my problem, I can't imagine what I will do to this bike.

    I will be ordering a new set of advance unit springs tomorrow.

    It reminds me of "stuckness" as described in Zen and the Art. Funny how the information I received led me to the answer even though the information was not exactly the direct answer.

    Thanks for leading me to (what I hope) is the answer. There are a lot of good ideas here. I will post after I have these things and let everyone know how it works out.
    beemerfield

  13. #13
    beemerfield
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    So - does anyone know anything about Hilderbrand?
    beemerfield

  14. #14
    Monza Blue 1974 R90/6
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    Congrats! I know how frustrating it is to chase a problem. I hope you are right and this is it. It will feel really sweet to ride it when it is running right knowing what it took to get there.

    Barron

  15. #15
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    The next question I would have now is just where is the missing advance spring or its remnants.

    If this junk is floating about in your points cavity you will continue to have problems

    Have some sharp eyed younger person take a good look in there

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