R100/7 High Idle after long warm up

Discussion in 'Airheads' started by Highwood, Apr 9, 2013.

  1. Highwood

    Highwood Been here awhile

    Joined:
    Feb 13, 2009
    Oddometer:
    119
    Location:
    Banff, AB
    Bike:1977 r100/7 43K Kms (no bean can, no electrics, mechanical advance)
    Bike starts well with choke, idles at 900
    After 2-3 km warm up, choke off, idles about 1100
    After 20-30 minutes of aggressive throttle, idle "sticks" at 2500-3000
    If I drag the rear brake to less than 2500 rpm, bike returns to normal 1100 idle
    If I turn off the key and restart, bike returns to normal idle
    Carbs have been rebuilt (all gaskets/o-rings/jets/needles/floats etc.). Mix, idle and balance set by 55-year-old, factory-trained bmw tech.
    Timing: seems good, but not personally verified by me, but the engine and bike are smooth and robust, no flat or dead spots in the rev range.
    Valves: good, properly adjusted including valve lash.
    Heads: retorqued and pushrod seals re-sealed
    Cables: in good repair
    Intake gaskets: no leaks per test with wd40, gaskets fresh in the last two years.
    Mechanical advance: carb cleaner, varsol dunk, silicone lube - seems ok, though "up-down" sloppy? But I have nothing to compare against.
    So, why does the bike idle high after 30 minutes of riding, but not after 10 minutes?
    Given I can drag the brake, force down the rpm mechanically and then it idles correctly or just turn off the key and restart and it idles correctly, that would seem to indicate a stuck advance mechanism. But, given I just cleaned and lubed the hell out of it, that seems like it can't be the problem.
    I have googled "site:www.advrider.com high idle r100" and read for the last two hours. I have read Snowbum's stuff. (Clearly brilliant, but he needs a good editor and to stop using bracketed after thoughts. As you will note, they ruin whatever flow may have been generated.)
    I am now more confused after the long discussions of jets, needles, choke gaskets (though they are actually an enricher circuit) 323 jets, in is richer, turn mixture out, too rich, too lean, leaking vaccuum, etc.
    What I know is I can't recreate the symptoms in the garage. High idle sticking only happens after 20-30 minutes of spirited riding. Bike pulls and runs great, pre and post high idle sticking. I can't tell it is going to do it until it does it, but it does it every time after the bike has been run hard.
    Please help, and if it isn't overly annoying, perhaps a step-by-step process to diagnosis and repair.
    I'm in Canada. The weather is still dodgy (-15C this morn, snow yesterday, +4C now).
    I promise to report back precise findings as I am able.
    I have a full rack of wrenches, feeler gauges, a timing light and a multimeter. I was raised on a ranch and I can fix stuff, but I am not an airhead or any other kind of guru. Just an eager, cheap, middle-aged guy that wants his airhead to return his affection.
    #1
  2. hardwaregrrl

    hardwaregrrl ignore list

    Joined:
    Jan 26, 2006
    Oddometer:
    9,104
    Location:
    Atlanta
    Didn't read that the diaphragms were replaced?
    #2
  3. photorider

    photorider Been here awhile

    Joined:
    Nov 24, 2008
    Oddometer:
    411
    Location:
    Southern Utah and Guatemala
    I hear you. It has all the symptoms of a stuck advance, no?
    Have you tried looking at it with the cover off?
    #3
  4. ME 109

    ME 109 Long timer

    Joined:
    Jun 25, 2009
    Oddometer:
    6,232
    Location:
    Albury Australia
    Back to normal after turning the engine off/on sounds like stuck advance.

    I like how the pros leave it up to us clueless to cover all the possibilities that end up having nothing to do with the problem. :D
    #4
  5. Highwood

    Highwood Been here awhile

    Joined:
    Feb 13, 2009
    Oddometer:
    119
    Location:
    Banff, AB
    Diaphrams were replaced with carb rebuild, a year ago in February.
    I have not inspected the advance while running with the cover off. I feel like I'd be tempting fate if I rode around for half an hour with the cover off.
    I'll get some heavy mitts and see if I can take the cover off next time it happens.
    What does a stuck advance feel like? Mine wasn't that physically dirty and the weights seem to move freely. I can grab some pix if that would be helpful.
    Thanks
    #5
  6. Kai Ju

    Kai Ju Long timer

    Joined:
    Jul 29, 2009
    Oddometer:
    2,855
    Location:
    Long Beach, California
    you don't have to ride it to see if the advance sticks, just start it up.
    make sure you pull the ground lead before you pull the cover so you don't fry a diode.
    #6
  7. Highwood

    Highwood Been here awhile

    Joined:
    Feb 13, 2009
    Oddometer:
    119
    Location:
    Banff, AB
    Just disconnected the battery, removed the front cover, reconnected the battery and fired it up.
    The advance weights seem to my eye to be moving correctly (spin out at higher revs, retract as revs lower).
    Please keep in mind, the bike is now almost stone cold and I used the choke to start it.
    Cold idle was about 950 rpm.
    Each side or each weight of the advance seems to feel the same; that is they retract - spring back - with about the same amount of force.
    There was a wee bit of white smoke when reving it high.
    Any other ideas?
    #7
  8. Highwood

    Highwood Been here awhile

    Joined:
    Feb 13, 2009
    Oddometer:
    119
    Location:
    Banff, AB
    Just ran my induction timing light.
    At idle is seems to be a few degrees below "OT" There is a wee paint fleck and a line in the inspection window.
    At high revs, it seems to advance to another convenient dot of paint.
    I don't know precisely where it should be timed, but it seems to be lining up on some properly marked bits so I take that to mean that it is timed correctly.
    Any other good ideas I can test in the garage?
    #8
  9. brittrunyon

    brittrunyon 1992 R 100 GS (ZED)

    Joined:
    Oct 6, 2010
    Oddometer:
    744
    Location:
    The High Desert of New Mexico
    #9
  10. 190e

    190e Long timer

    Joined:
    Feb 20, 2013
    Oddometer:
    1,528
    Sticking advance mechanism is a possibility but idle hang up can also be carb related even when they have been set up by a pro. In fact is much more often carb settings rather than the sticking advance.

    1100 RPM is a touch high which can start the transfer ports flowing some mixture. Try turning the idle stop screws out by very small equal amounts to drop the idle speed to 1050 RPM.
    #10
  11. supershaft

    supershaft because I can

    Joined:
    Sep 9, 2010
    Oddometer:
    9,116
    Location:
    San Francisco Bay area
    +1 They all do that when the idle is set too high and/or the mixture screw too lean. Idles at around 900rpm damn near stone cold? Of course it idles fast when it's hot. Idle speed all depends on what 'a lot of throttle' is to you. If I want my bikes to idle at 1000rpm after they have had 'a lot of throttle', I need to set the idle idle speed to where they won't idle at all after a couple of km's. If I had my idle speed adjusted to idle around 1100 rpm after 2-3 km's warm up my bike would fast idle like a mofo once it got good and hot. They all do that. It's an air cooled engine.
    #11
  12. ME 109

    ME 109 Long timer

    Joined:
    Jun 25, 2009
    Oddometer:
    6,232
    Location:
    Albury Australia
    It is easy to be caught out by too high idle screw setting.
    2-3000 rpm is beyond what I've experienced from too high setting tho'

    Backing the idle screws out is a damn good place to start.
    #12
  13. Plaka

    Plaka Brevis illi vita est

    Joined:
    Jun 19, 2010
    Oddometer:
    4,641
    um...learn what the timing marks mean and make sure it is doing the correct thing at the correct mark.

    If you think the weights might be sticking it is trivial to lube them, So do that, Then you know they aren't sticking. If recently lubed, unlube them.

    Make sure your throttle lock screw isn't set.

    You say it doesn't idle high after 10 minutes. You don't say 10 minutes of what. 10 minutes of hard riding? Easy riding? idling in the driveway?

    What kind of oil do you have in it?

    What did the mechanic who worked on it say?
    #13
  14. Plaka

    Plaka Brevis illi vita est

    Joined:
    Jun 19, 2010
    Oddometer:
    4,641
    You always disconnect the battery before removing the front cover.

    You can run it with the front cover off. The points like to stay clean tho, avoid, water, oil and lots of dust. Clean them with alcohol after running open. With it off observe the resting position of the weights. Then rev. it with the timing light pointing at the points and watch them do their thing.

    Try holding it on cruising rpm in the driveway until it gets as hot as it does with your "hard" riding. What happens? This train of thinking goes along the lines of a thermal issue.

    Springs can be weak, advance shafts can be worn, etc. As a rule an electronic ignition and never screwing with points again is a good investment. All the systems That I know of that replace points allow you to convert back on the roadside if you need to.

    You can also have a sticky carb slide/cable/butterfly. When you shut it down you not only close the throttle but the vacuum stops. A finger lifting and releasing the slide says much...but do it with the bike hot.
    #14
  15. Solo Lobo

    Solo Lobo airhead or nothing

    Joined:
    Mar 16, 2004
    Oddometer:
    10,021
    Location:
    Shoreline, WA
    One more check for something simple:

    Push down on the arms of each choke where it enters the carb. I had a bike with a similar behavior and found that one chock wasn't returning to the full "off" position and was hanging up.
    #15
  16. Highwood

    Highwood Been here awhile

    Joined:
    Feb 13, 2009
    Oddometer:
    119
    Location:
    Banff, AB
    Thanks for the suggestions and links.
    More twiddiling in the garage last night revealed the following:

    Timing: There is a "ghost image" at the s mark (idle timing mark) giving me two lines and two dots, perhaps a degree or two apart. The ghost image is kind of like someone rapidly shaking a pencil. I taped the weights closed (no advance possible) and retested and still had a ghost image. I take this to mean that ignition timing is not identical on both sides.

    ATU: Clean. Spring return is good. Everything loose and easy moving. With a timing light, advance (weights out) and return (weights in) seems smooth, though perhaps a slight "hang" on the last moment of return (less than 1500 rpm), but it was late, I was tired and if there was a hang, it was mild and brief. Advance shaft is smooth over its entire depth and has no horizontal streaks or marks, suggesting to me that it is not unduly worn. Bike only has 44K kms (27.5k miles).

    Points: Gap seems to be too narrow. .35mm gauge will not fit. Removed and inspected. They look pretty vintage, pitted on both sides, but the pitting seems relatively centered. Pitting has not eroded the edge of the contacts, just the centre. The black rub bar seems quite short (but I have nothing to compare to except past dealings with old Fiats and Porsches.)

    Plugs: Quite black and sooty, as distinct from oily. Consistent with a "rich" condition or poor ignition according to my Haynes manual. Plugs are a perfect match to the picture in the manual. That may have been due to my carb settings, rather than the tech's carb settings. I only have about 150 kms on the bike since the tech set the valves and carbs.

    Timing Chain: I assume if the problem (different ignition timing side to side as indicated by the ghost image at idle) is timing chain slop, I would hear it with my head between the wheel and the front cover, or laying under either cylinder. There is no slapping, clanking or chain-like noise, just a gentle tick-tick of the valves.

    Camshaft Nose: Shaft looks good. No visable signs of wobble or bending. How does one determine if the camshaft nose is out of true?

    Exhaust: Bike has two-into-one exhaust installed by previous owner. Metal gaskets and fin nuts are good, tight and leak free. Heat feels "equal" from both cylinders, but I can juggle baked potatoes. I don't trust myself to be able to determine if one side is hotter than the other.

    Intake: WD40 test shows no leaks. Vacuum port screws snug and seated. No air or vacuum leaks at the carb or manifold.

    Choke return is to full stop on both sides.

    I'm gonna chase down new points and a new condenser, install, gap correctly, check and adjust timing and report back.

    If new points and condensor result in the same idle ghosting, I will also adjust idle downwards (screw out) to see if I can reduce the warm, not hung, idle and report back. I can imagine a scenario where too fast at idle would result in a rich condition. I can also imagine a scenario where high idle would increase as bike got warm, especially if the "transfer ports" are engaged.

    Regarding the question of hard riding, I am gentle with the bike until I can turn the choke fully off, about 2-3 kms. After that, I use 2nd and 3rd gear and my right hand. Part of the point of a motorcycle is to get through traffic efficiently. I'm not cruising generally. I am briskly accelerating and decelerating through traffic, pulling the engine near redline regularly. The "hang" seems related to the last steady-state throttle position. At fast or hung idle, the engine still feels and sounds balanced. There is no right-hand torque or unusual vibration.

    I have an R12GSA for making miles. I use the Airhead around town as a cool, relatively-high-speed grocery getter and errands mobile. That being said, I am the only guy I know with an airhead. I have never ridden another airhead. My impressions may lack context.

    I am out of town for a week, so if I go dark, it just means I haven't had time to do the work. I'll report back at my earliest.

    Sincere thanks for the suggestions, thoughts and links.
    #16
  17. Plaka

    Plaka Brevis illi vita est

    Joined:
    Jun 19, 2010
    Oddometer:
    4,641
    Pressed for time at the moment.

    You have bent cam nose. The symptom is the double image. Confirm it with a dial indicator if you want.

    Not likely to be your problem. You can kind of split the difference when timing it or Try to straiten the nose (interesting thread on that recently), or fit an electronic ignition. I chose the last on my /5 as I was dual plugging anyway.

    Do plug chops to evaluate the mixture when you are running at speed and having the problem.

    Know what a points file is?
    #17
  18. 190e

    190e Long timer

    Joined:
    Feb 20, 2013
    Oddometer:
    1,528

    Plugs can't be read reliably if the choke has been used as it can soot them up even when the normal running mixture is correct. Most reliable method is to put clean plugs in engine that's already hot. Having said that I'm not too keen on risking the threads when the engine is hot so if it's possible start and run without choke I prefer to do that.
    #18
  19. Highwood

    Highwood Been here awhile

    Joined:
    Feb 13, 2009
    Oddometer:
    119
    Location:
    Banff, AB
    I believe the pitting is too severe to be addressed with a points file. Just ordered points and condenser for arrival late next week.

    I'm uncertain what you mean by "do plug chops to evaluate the mixture." Help please.

    There is no ghosting at the full advance mark with the old points, just at idle. Does that change your view on the bent camshaft nose? Alternatively, given no ghosting at full advance, does that mean the bend is small enough not to be having a significant impact? Or, does the bend mean that carb balance is virtually impossible because one is using mixture to try to compensate for unequal left to right ignition? Is it possible there is a bearing going that could cause the camshaft nose to wobble? Can that bearing be fixed easily?

    I'm reluctant to throw $300 at an electronic ignition, but I love the bike. Is there consensus on the best electronic ignition? Dyna or Omega? Or, are both good and I am asking the equivalent of "what oil should I use and how often should I change it?"

    Thanx for your help.
    #19
  20. disston

    disston ShadeTreeExpert

    Joined:
    Mar 22, 2011
    Oddometer:
    13,595
    Location:
    Silver Spring, Md
    A ghost of one or two degrees is supposed to not be a problem. I think I read that on Snowbum's site when I was dealing with this problem some years ago. But in principle I will tell you that it would bother me. I ended up with a solid image, no ghost, after doing the bent cam tip explained on the Duane Ausherman site.

    http://w6rec.com/duane/bmw/timing/

    That link is for the article about the double timing image. There is a lot of info on the DA site but this article is hard to find. He is talking about /2 BMW's but the principle is the same. It might be a good thing to point out that a timing image that spans the beginning of one tooth of the flywheel to the beginning of the next tooth is more than 3 degrees.

    At one point I had the double images touching each other but I was able to get them closer than this. When I started the images were so far apart that it looked like one image till the throttle was raised and the second image could be seen. My BMW sounded more like the lope of V twin motor (you know what I mean?) :lol3
    #20