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Thread: 93 R100R intermittent power loss on long trips

  1. #1
    Registered User 101736's Avatar
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    93 R100R intermittent power loss on long trips

    I am experiencing a long-standing intermittent problem on my '93 R100R. I finally am concerned enough to dive into this as time permits, and I'd appreciate any suggestions for possible causes and potential resolutions.

    The problem I'm having only seems to exhibit itself during long trips, meaning after several consecutive 500+ mile days. I'll be running along at speed and the bike will lose power. It feels as if it were running out of gas, however switching to reserve has no consistent effect. The bike will slow to 65 or 60mph and maintain that speed, even thought the throttle is fully open. It's running poorly during this, feeling and sounding bogged down. After a mile or so, full power resumes. It may or may not happen again in a few miles. This has been an occasional but ongoing problem for 3 or 4 years now.

    I've always assumed the issue was fuel-related because it invariably seems to happen in the Midwest (high-alcohol fuel, 2 days from where I live); because it usually happens 10 to 12 miles into a new tank and again 60-80 miles into the same tank; because last year it occurred just after I had to remove the cross-over fuel line due to a leak as I passed through KC; because when power resumes there is no back fire (which to me would indicate an ignition problem allowing the fuel to load up). I've tried lifting the tank bag (RKA bag with plastic bottom) up off the gas cap when the problem occurs, and it has no affect.

    I use this bike for weekly grocery shopping (local, non-highway) and touring. This season I took 2 trips: a 5-day Georgian Bay circumnavigation (2500 miles) and a 7-day journey to the Return to Shiloh Rally (3200 miles). The problem only occurred during the 2 days it took me to ride home from Shiloh on the interstates. That the problem started happening in Kentucky rather than in the Midwest this year makes me wonder if it is after all an ignition problem. But why didn't it happen in Ontario? It happens rain or shine.

    The bike is a '93 R100R with 105k miles on it. Engine was replaced after seizing at about 25k. Drive shaft replaced at 85k. Transmission re-shimmed at 100k. I still have the original frame.

    As far as electrical components are concerned: voltage regulator replaced at 45k, rotor replaced at 50k (open), plug wires are 7 years old, diode board preemptively replaced with Motorad Elektrik version also 7 years ago, starter replaced for the 2nd time (with ME ND starter) during the Boise RA rally in '06.

    I rebuilt the carbs several years ago but they stink and occasionally leak, so it's time again and I'll do it this winter.

    This week I've cleaned and lubed all electrical connections under the tank and behind the front engine cover, removed and inspected the coil with resistance values in specification and no obvious cracks or arcing, and I cleaned the petcock screens (which weren't that bad, although the red paint is starting to flake off the interior of my tank). I haven't had time to run it since and don't expect the problem to re-exhibit itself anyway until my next long trip.

    I'm considering just biting the bullet and replacing the coil, ignition module and Hall Effect sensor, but the expense makes me shudder almost as bad as the bike when it's straining to hold speed. Your diagnostic thoughts and suggestions are sincerely appreciated.
    Chris near Boston

  2. #2
    Registered User mneblett's Avatar
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    I had what sounds like the identical problem on my '94 R100R Mystic. After verifying that the tank was properly vented to atmosphere (so that it wasn't an issue of vacuum building up in the tank to prevent fuel outflow from the petcocks), I ultimately found the issue to be that the floats were set a hair too low, so that one or both bowls ran dry when doing 70-75 mph. Reset the floats to the correct height, and no problems since.
    Mark Neblett
    Fairfax, VA
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  3. #3
    Cave Creek AZ 85k100lt's Avatar
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    has to be a reason

    I would suspect a carb problem. Does this happen under load such as a long gradual uphill climb. I know not a lot of elevation change in the midwest but a incline that slow and long could effect the carbs float/ vaccum diapharms.

    I would rebuild the carbs first with new diapharms.

    Just my 2 cents worth.
    1974 R75/6 W Sidecar
    1989 R100GS


  4. #4
    SGRIMSON
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    Had the same problem

    It was found that my plug wires were dried out. They are recommended to be changed every 5 years anyway. The mechanic just grabbed the wires and bent them and looked for the rubber coating to fray. It did. New wires solved it. I must admit though, that the stumbling still does happen at about 90 to 95 MPH. Another reason to slow down, eh? (1984 R80 RT)

  5. #5
    Registered User toooldtocare's Avatar
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    My guess, poor venting in the tank. Check the vent hoses and the emission valves (if they are still there) to be sure that you are not developing a vacuum in the tank. Easiest way is to just loosen the gas cap when this happens. If the problem clears up in a few seconds, that is the issue.

  6. #6
    Bill Burke
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    Long shot but have you every replaced the throttle cam gear and throttle tube on the handlebar? I'm thinking potential slipping issues with a worn cam/tube teeth.....

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    worn needles in the carbs can cause a fluctuation at highway speeds also.

  8. #8
    R100GS, '89 Guenther's Avatar
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    I would take the petcocks out. Could be some paint flakes collected around the mesh and slosh around and may cause a near blockage.

    Wouldn't hurt to remove/inspect the whole main/needle jet assembly for dirt. Although I would think this would cause a more permanent problem.

    Both are quick and things to do.

    If you still have the emission gadgets installed, check that the plug that connects the tank vent to the air filter box is not too close to the left side "suction funnel" (the big black hose in the airfilter box). Could eventually block the venting of the tank.

    /Guenther

  9. #9
    Registered User boxerkuh's Avatar
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    I can relate... it turned out that one of the float bowls was a little low... so I would start out with the carbs and from the sounds of it... it is on your list to do this winter. After that, I would check the diode board... make sure all the connections are good... they do fail at times... That is a great bike you got!!!
    Keep the rubber side down!!
    1986 R 80 RS
    1992 R 100 R
    BMW MOA Life member; Ironbutt Member; Airhead Member

  10. #10
    Registered User 101736's Avatar
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    Thank you all

    for your great kindness in taking the time to respond to my posting. It seems that the majority of you suspect fueling issues. That's where I'll focus my efforts.

    I have some questions about some of the suggestions. I address my questions to particular people but if anyone has opinions about anything I'd like to hear them.

    Mark--you suggest verifying the tank is properly vented. As I understand it, the tank is vented through the cap. Is there a procedure to bench test and verify the cap is properly venting, or must I wait until I experience the problem and then unscrew the cap? Should I just go ahead and drill the cap as suggested on Snowbum's page? Any drawbacks to that?

    I like your idea of the carbs running dry because the floats are too low. Not sure how that applies to my very intermittent problem, though. A carb rebuild is on the agenda and I will pay particular attention to that.

    85K--I suspect a carb problem too, even if it's not the cause of my primary concern. I rode the bike to work today and remembered another symptom not previously mentioned: if I don't blip the throttle at stops or I'm not extremely careful as I roll it on, the bike will stall. This problem is new this season. So some adjustment is necessary. I can't connect my primary concern with any particular terrain--and the land is quite varied where I live--just long trips.

    SGrimson--my plug wires look good but I will consider replacing them anyway. I don't think you should slow down.

    TooOld--does the tank vent through the hoses attached to its bottom side? I thought they were only for draining overflow, and that the tank vented right out the top of the gas cap. Do you see any drawback to drilling the cap for venting?

    What are these "emission valves" of which you write? The bike once had hoses connecting the air box to the exhaust headers (clean air injectors? they were for emissions, anyway) but they are long gone. If these are what you're referring to, I don't understand how they'd be involved in this issue if the bike were still equipped with them.

    Bill--I still have all the original control cables on the bike. I'll examine them all over the winter, especially the throttle mechanism.

    Ton--I will check the carbs. Don't you slow down either!

    Guenther--I did remove the petcocks Tuesday night. There were a few flakes and they're gone now. Maybe there are a lot of flakes mixed up with the gas now that I turned the tank over. It ran OK on the way to work this morning, though. Carb rebuild coming up! The emissions tubing is long gone. I had no idea there was once a connection from the tank to the airbox.

    Boxerkuh--Another vote for low fuel level in the bowls! Thanks for complimenting my bike. It hasn't been what one would call "reliable" but I love it and it reflects its owner's personality, ie. "unreliable."

    Brewmeister--Feel like talking politics? When are you coming east?

    Again, my sincere thanks to each of you!
    Chris near Boston

  11. #11
    Registered User toooldtocare's Avatar
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    On the newer bikes there is a bunch of stuff in the airbox that controls venting of the gas tank. It is a sealed system, the gas cap will allow air in, but not out unless an excessive pressure is formed in the tank. This prevents it from over-pressuring itself.

    In the airbox are solenoids that control the venting of the tank (to the engine case when it is off), thus vapors do not excape (or so they say). Another solenoid shuts off the gas.

    Many riders (myself included on another bike) had trouble with the solenoids and removed the system. We then ran a separate vent to the tank that relieved the need to suck air through the gas cap in case it got clogged up.

    Under Fuel and Lubrication Sytems in the Haynes manual there is a good explaniation of the system. Good luck.

  12. #12
    Registered User mneblett's Avatar
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    Quote Originally Posted by 101736 View Post
    Mark--you suggest verifying the tank is properly vented. As I understand it, the tank is vented through the cap. Is there a procedure to bench test and verify the cap is properly venting, or must I wait until I experience the problem and then unscrew the cap? Should I just go ahead and drill the cap as suggested on Snowbum's page? Any drawbacks to that?
    I would not drill the cap, particularly since the works/doesn't work test is so easy: Next time the engine bogs, screw open the gap a ways to raise the cap's upper seal off the inner filler neck so that air can enter the tank past the cap threads. If the bike begins running well again in ~10 seconds because the vacuum has been relieved, you may have a cap problem -- I doubt it though, as the later emissions caps didn't regularly fail. I tried this first (even positioned the cap handle so that I could quickly/easily twist it open a turn or so at speed), and it confirmed it wasn't the cap.

    Quote Originally Posted by 101736 View Post
    I like your idea of the carbs running dry because the floats are too low. Not sure how that applies to my very intermittent problem, though. A carb rebuild is on the agenda and I will pay particular attention to that.
    This is why I think it is a float problem, and not all of the other straw-grasps above.

    My problem was also intermittant, and always cleared after 30 sec.-1 min. -- due to the bike slowing and the bowls refilling. My problem only occurred when fuel demand was very high -- usually a couple minutes after wicking it up to 70-75 (I could run all day at 65 with no problem), or at slightly lower speed with a full load and going uphill. When the bike started to bog/stumble, the bowls would have a chance to refill, and then I would either ride at 65 (no further problems) or would ride again at 70-75, which would cause the problem to recur within a couple minutes.

    While many of the suggestions above are earnest attempts at helping, most have the problem of not fitting the symptoms either well or at all -- either they would be causing constant problems, or a different behavior would be produced. If it were not for the symptoms, I would have suggested that the electronic ignition is overheating (due to heat transfer paste needing to be renewed), but the symptoms don't fit -- the ignition would not recover so "cleanly" within a minute or so of the bogging, because the ignition module wouldn't cool so quickly.

    As Sherlock Homles would say (paraphrasing): Fit the theory to the facts!

    So, I would start with the floats -- easy to do with the carbs on the bike. It is also something than can be done with no need to wait for/do a (likely unncessary) full carb rebuild.
    Mark Neblett
    Fairfax, VA
    #32806

  13. #13
    R100GS, '89 Guenther's Avatar
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    If the PO did not remove more emission stuff... the tank cap is sealed. The tank vents through a hose (#5) underneath the tank to a solenoid (#11). This side of the solenoid has a T-connection with the other T-side going through a pressure relief valve (#15) into the crankcase. The switched side of the solenoid extends through a hose to a pipe (#17) in the air filter box:

    http://www.realoem.com/bmw/showparts...41&hg=16&fg=05

    With ignition off the tank can only vent into the crankcase if a certain high pressure is reached. There it allows the gasoline fumes to condensate into the engine oil. With warmed up engine the gasoline evaporates again and is forced through the crankcase bleeder finally into the carburetors and finally burnt.

    With ignition on the solenoid opens and the tank can now vent (in both directions) through the air filter/ carburetors. If the motorcycle has been parked in the open sun one can typically hear the pressure relief through the valve just when the ignition is turned on.

    So, if the little pipe is blocked by the left suction funnel (big black hose) in the air filter box the tank can no longer "breath" air. I had that frustration on my way home from the 1st inspection of my R100GS. The mechanic was careless when assemling the parts in the air filter box thus blocking that "pipe". Opening the filler cap a bit at least let me make it home the remaining 60 miles.

    Btw. the same effect would happen if that solenoid would fail to work (inner mechanical problem or, more likely loose wire contact).

    Good hunting!
    Guenther

  14. #14
    Registered User 101736's Avatar
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    Air box solenoids

    are long gone. All that stuff failed to make the transition when the replacement motor was installed at 25k miles.

    Thank you Guenther for the explanation with link to parts diagram. In this case most of that does not apply, however I assume there could still be a problem with the cap failing to vent via the hose hook-up on the underside of the tank.

    Interestingly, the bike choked as I got on the highway shortly after I accelerated to commuter cruise speed for my ride home last night. That surprised me, it's only supposed to fail on long trips, but I don't normally use this bike for commuting.

    For now my working assumption is that float levels are too low. I appreciate everyone's suggestions.
    Chris near Boston

  15. #15
    Registered User toooldtocare's Avatar
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    If all that stuff is gone, than there is an extra vent coming off the tank. On my bike, I ran a separate hose to the back of the engine, and I bet the PO did the same for you. If this is the case (that is he did not plug it), you can rule out the gas cap since you now have a hose venting the tank.

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