R100GS sputtering at speed

Discussion in 'Old's Cool' started by Cirbo, Nov 18, 2009.

  1. Cirbo

    Cirbo Been here awhile

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    Ok, I took off early last Saturday to chase a tag about 60 miles south of the house. I slabbed it for most of the trip to get there and back before being bruced, so most of the riding was at 70-80 mph. While the bike (a 1990 R100GS) runs like a top at most all speeds, I had an interesting occurance at the higher end. When going from 75 to 80 passing traffic, the motor would occasionally cough and sputter a bit. I couldn't attribute it to anything in particular, and it would only happen at that time (and not all the time). At those speeds, I was only able to feel the hesitation, not hear any accompanying noises.

    The two thoughts I had were carbs, or ignition. Can anyone give me any good troubleshooting thoughts or ideas?

    TIA,

    Jim
    #1
  2. bgoodsoil

    bgoodsoil Dare to be Stupid

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    some clogging on the main jet? shut off the fuel and drop the bowls. If you see anything but nice clean aluminum anywhere it might be time for a cleaning. Heck even if you don't you can hose some carb cleaner through the jets.
    #2
  3. datchew

    datchew Don't buy from Brad

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    test your hall sensor. just get it over with.

    If you don't want to think about that option (and I don't blame you) then try a fresh tank of gas and do the basic tuneup. Valves, timing, carb balance, plug check, etc.
    #3
  4. Cirbo

    Cirbo Been here awhile

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    Interesting.... I guess "Search" is going to be my friend on this matter. Looks like Datchew has many contributions to this subject matter. A quick look leads me to another possible symptom. The RPM's seem a little slow to return to proper idle too....

    On a related note, the carb bowls are spotless, and the plug wires are the type with the metal caps on the end (OE?)
    #4
  5. StephenB

    StephenB G(/)S ... what else!

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    Float bowel level is my initial thought ...
    #5
  6. Cirbo

    Cirbo Been here awhile

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    Too low, and starving for fuel at speed?
    #6
  7. bgoodsoil

    bgoodsoil Dare to be Stupid

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    yeah but float level doesn't usually change for no reason. Is this a sudden problem or did it start after doing something in the carbs? Does it always happen when accelerating on the top end or is it intermittent?
    #7
  8. Cirbo

    Cirbo Been here awhile

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    I changed the float bowl gaskets shortly after getting the bike (6-8 months ago). Most all of the mileage I logged has been on back roads and secondary highways. I sensed one quick miss some weeks ago while traveling at ~70-75 mph. Saturday's trip was the first at sustained highway speeds. As I got outside the city where the speed limit ratched up to 70, I began to feel the slight misses when passing. It seemed to get a little worse as the day/mileage went on, but disappeared when I reduced speeds back to normal levels.

    I can't say that it always happens when accelerating at top end, but I can say that it's the only time it happens.:huh
    #8
  9. outfit

    outfit Been here awhile

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    Mine too.

    Karl.
    #9
  10. ChromeSux

    ChromeSux Plated and screwed

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    Mine was acting almost the same when i bought it, mine turned out to be that the red primer type paint was coming loose in my tank and clogging the petcock screens in the tank, flushed the tank a few times and put new screens in and problem gone.
    Now once a year i flush out the tank and get more red stuff each time, so much red paint came out the first time i could not believe it.
    #10
  11. Scott Davis

    Scott Davis Which way did they go?

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    I have a 92 model and just rebuilt both my carbs. I am pretty good at setting them up, PM me if you would like some local help!

    I think the float level would be my first check, then balance carbs. While in there, blow out all the jets and ports. Can't hurt!!!

    :)

    Scott
    #11
  12. Cirbo

    Cirbo Been here awhile

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    Would the PD tank also have red primer (being poly)? This is the second time I've heard that idea.
    #12
  13. ChromeSux

    ChromeSux Plated and screwed

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    I am not sure i havent looked inside a PD tank, BMW used the primer like coating for many years, some of these other guys will know for sure.
    I know my R75/5 and my 1989 R100GS has it inside.
    #13
  14. browncycle

    browncycle two-up tennessee

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    I have an '82 R100 RT that is now an S and I had a similar problem a couple of years ago. Only ever on the interstate (which is rare for me) or once passing a car up a hill. This was in '07, when it was ridiculously hot. I took it in to my local dealer and had them look at a charging issue and asked them to adjust valves and synch carbs, as I felt I was overdue for that anyway.

    It hasn't done it since.

    And the charging issue taught me that the red bulb in the instrument cluster is part of the charging system. No one ever told me that before.
    #14
  15. bgoodsoil

    bgoodsoil Dare to be Stupid

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    It was a genius that came up with that one right? I'm not an engineer and I hate to badmouth somebody's work but whoever designed that is a moron. Whoever left it that way for decades is even dumber.
    #15
  16. datchew

    datchew Don't buy from Brad

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    [snobby british accent]Good show old man. [/accent] :thumb
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  17. datchew

    datchew Don't buy from Brad

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    There are morons in the engineering world. Trust me... I'm one of them sometimes. :freaky:huh
    #17
  18. jeveretts

    jeveretts Foilhead Extraordinaire

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    Did you ever get this problem sorted out? I am having the exact same issue with my r100gs 1992
    #18
  19. durtwurm

    durtwurm Talented Amateur

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    Check your diaphragms as well! Take them out and look for holes next to a bright light.
    #19
  20. Tim McKittrick

    Tim McKittrick Long timer

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    No one has mentioned fuel filters yet- I chased a similar issue for some time with my R100RT and after going through float settings, valve adjustments, timing, coils, petcock filter socks, and tank and carb venting I finally changed the fuel filters. In my case, the old filters appeared fine- they looked new and had no visible buildup of crud in them, yet they were just restrictive enough to starve the bike for fuel under just the right conditions. Pulling a hose off a carb and opening the petcock appeared to produce plenty of flow as well, and if there was more than a half tank of fuel it was fine because of the added fuel pressure from the full tank. Now whenever I hear of someone having a high load stumble I suggest looking at the filters FIRST- they are by far the easiest thing in the system to change, and cheap to boot.
    #20