Help Diagnosing R100GS Running Issue

Discussion in 'Airheads' started by coloduc, Jun 14, 2018.

  1. coloduc

    coloduc n00b

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    After about a year of searching, I finally found something I've wanted since I was a kid: an R100GS in decent shape for a not insane amount of money. Have been picking away at the usual little issues on an old bike and I've come across a mystery: There's a two-prong plug on the right side of the engine block (right under the tank and in front of the airbox) with nothing plugged into it.
    [​IMG]
    I don't know what it's for so search has been unhelpful. Can anyone tell me what that is, and if there should be something plugged into it?

    The bike runs well, but is extremely vibey under acceleration. It doesn't start as well as I'd expect: requires precise throttle input to start, then I have to hold the throttle open for 1-2 minutes or it'll stall, regardless of temperature or choke position. I've had the bike run through, the carbs synced and had a bad pushrod replaced. Would welcome any thoughts about the vibes. I know the 100 is a buzzier engine, but when on throttle, my eyes go blurry, so I assume it can get better than that.

    Thanks,

    UPDATE: Thanks to everyone who helped solve the mystery (of a partially intact pulse air system). The rough starting and poor running continue. I've added a video on pg 2 in the hope that someone can help diagnose the funky air/vacuum noise which seems to be getting worse, as does the starting and vibration at idle and under power.
    #1
  2. Solo Lobo

    Solo Lobo airhead or nothing Supporter

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    Ditch the in-line filters to start with, could be you have a fuel delivery issue and the bike is only running on one side.

    If it is that vibey, your carb balance is not right, among other possible issues such as valve adjustment, bad plugs, wires, etc...
    #2
  3. Joel1

    Joel1 Been here awhile

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    The hole was for some pollution control parts. The spades that are visible are for the fuel control solenoids that are now bypassed. Someday when you take the tank off, pull that cover off, remove the bits that are no longer being used, plug the holes, paint, and replace the cover. Or, you can leave it as is and not worry about it.

    I glassed behind the holes on mine then filled with fibre reinforces bondo.

    When I bought my GS new in 89 it had all that stuff.

    Joel
    #3
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  4. Solo Lobo

    Solo Lobo airhead or nothing Supporter

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    The starter covers without holes are available on eBay for cheap... I have never actually seen one of the covers with the holes in person (yet).
    #4
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  5. coloduc

    coloduc n00b

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    Excellent, thanks! Just glad it isn't something important. I'll replace the cover as soon as I run out of other things to fix.

    I'll start with the fuel lines tonight (the filters do look old and the lines were on my list anyway). I haven't been lucky with an easy fix in a while, really hope that helps.
    #5
  6. Uke

    Uke visualist Super Supporter

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    Be prepared for a bit of a struggle getting the crossover fuel line from one side to the other.

    Save your Tee's, they're usually reusable. Before removing the existing crossover, stick a piece of chop stick or something else that will connect the new fuel line with the existing line and then push - pull guide the new line across the engine. A worst case scenario will necessitate loosening the air box, (two horizontal bolts through the front corners and a single vertical bolt about in the center) to create some extra clearance to get the new line from one side to the other.
    #6
  7. bmwrench

    bmwrench Long timer

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    That plug is the top of a solenoid. There were two of them; one for fuel flow and the other for fuel tank ventilation. These were to meet Californias "Shed Test". in which a vehicle had to be able to sit idle (not running) and not emit above a certain level of hydrocarbons. This is also why the bikes of that era also had the curious strap bolted to the bottom of the tank: With the tank unable to vent, it would pressurise, and the tank would spread until it split.
    #7
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  8. akabeton

    akabeton Adventurer

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    Welcome to the asylum.
    Lots of great folk on here.
    Let’s see some more pics of the bike.
    #8
  9. Warin

    Warin Retired

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    A GS .. paraleaver ... could be the shaft. Try backing off the rear shock preload so the shaft runs more flat and see it the vibes reduce.

    The cold running/starting would suggest something wrong with the chokes .. possibly the left side choke mechanism is in inside the right ... they don't like that.

    Fuel supply can easily be judged - pull off a float bowel and measure the rate of fuel flow, say how long a quart takes to come out. Repeat for the other side ... now estimate how long it would take to flow a gallon .. then figure out the fuel consumption per hour and if the engine would ever consume that much fuel ever.
    #9
  10. coloduc

    coloduc n00b

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    Thanks for all the input so far. I got most of the fuel lines replaced before dark last night. It turns out that the crossover tube is still connected to the solenoid under the starter cover and I didn't have time to pull that off and re-run that line. Did a bunch of research on removal of the Pulse Air/SHED system and it seems that all components are still attached (pipes to the heads and hoses to the solenoids). Everything is still connected to the solenoids except the solenoid wires. Wondering if that could be contributing to the starting/running issues?

    This morning, of course, the bike was extremely hard to start. I think it's getting worse: seems to need a very precise amount of throttle on the first attempt. If I don't get that quite right, it's several minutes of fussing before it'll catch.

    I listened very closely while it was idling and there's a sound from the right side of the engine that sounds a bit like a vacuum/air pulse between the usual chugging/ticking (sort of a rapid ptchsk). The idle when cold is also still pretty rough in general.

    While I was hoping to hone my mechanical skills with this bike, I think I expected a more gentle ramp up. Into the deep end we go.
    #10
  11. luxlogs

    luxlogs Bespoke BMW Bits

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    Naw you aint deep yet, just wadeing. These problems are a blessing for you to get to know your bike. You bought it to wrench on so get wrenching and join The Airheads.
    #11
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  12. brg

    brg 1977 XT500, 2000 ST1100, 1995 r100r Mystic

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    Yeah, get rid of all that emissions bs. Ted Porter at the Beemershop https://www.beemershop.com has a kit to remove and plug all the various holes. Very convenient, to have it come in a kit with everything you need. Chunk.
    #12
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  13. Uke

    Uke visualist Super Supporter

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    Ditto!

    Open up the starter cover and the air box (air cleaner enclosure) and get all the pulse air / emissions plumbing and associated crap out of there.

    Snowbum has a lengthy discussion (apologies for the redundant adjective) of the process. It's worth the read.

    http://bmwmotorcycletech.info/pulseair.htm
    #13
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  14. atlthrux

    atlthrux Been here awhile

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    Here's another parts list in case you can get parts locally.

    My r100gs PO didn't completely remove all of the pulse air stuff. One the pipes leading from the cyclinders, he just pinched them closed near the cylinders & cut off the rest. On acceleration, only when running, I got the vibration effect. Not an eyeball rattling one like yours but one worth investigating. Until you get a chance to remove the stuff check to see if those lines are all closed tight.
    #14
  15. airheadPete

    airheadPete Wherever they send me. Supporter

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    Snowbum = lengthy? Bite your tongue! :thwak
    (Though his information is great.)
    #15
  16. bmwrench

    bmwrench Long timer

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    No disrespect intended, but Snowbum's site and posts remind me of the old line about putting a bunch of monkeys in a room full of typewriters. Eventually, one of them will write The Great American Novel.
    #16
  17. Uke

    Uke visualist Super Supporter

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    Every time I venture into the morass of Snowbum's site, I long for the good old days of monochrome computer monitors.
    #17
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  18. QueensHorseman

    QueensHorseman Adventurer

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    There is a good blog you can find by searching the web for “gunsmoke bmw”. He has a great tutorial of removing the air pulse system from a r100gs with pics and part numbers. When I did mine, everything turned out super easy. Timing hole rubber plugs fit the airbox and the oil drain plugs fit the head so parts are easy to source. All of that stuff has been removed from my ‘94 but I would like to replace the starter cover at some point to get rid of the holes required for these systems. On the blog, he welded and refinished his cover but I’m not that handy and would just replace it.

    Are there any specific years that work best for upgrading / replacing the starter cover?
    #18
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  19. bmwrench

    bmwrench Long timer

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    '81-'84
    #19
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  20. ME 109

    ME 109 Long timer

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    Ha, I'm looking at putting holes in the starter cover. Funny stuff, this airhead business.
    #20
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