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Thread: 95R100RT won't idle consistently

  1. #1

    95R100RT won't idle consistently

    Just turned over 35K and decided to replace the OEM throttle and choke cables thinking long enough for the originals and why take a chance. Adjusted valves, air filter clean, timing set, new plugs, wires tested this year while the carb floats and diaphrams were replaced last year. Bike was running fine prior to my cable replacement Now the idle when fully warm will be fine for a short time 1-2min, then get rough for 20 secs or so, then smooth out and continue in this pattern. It is especially rough if after a spirited ride on freeway and then exit--get to bottom of ramp and while stopped at idle, shakes horribly. I have replaced the idle and mixture o rings, cleaned these parts 3 times and their seats along w/compressed air and did a carb sync with TwinMax. Starts right up, has great power and smoothness, just cannot get the idle to stay consistent. Any thoughts? Hate to replace the idle mixture, spring, idle jets and O rings if not needed. Thanks for any help my way. Jim

  2. #2
    Registered User toooldtocare's Avatar
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    Mar 2008
    DeLand Florida
    If it was running fine before, than something you did to it is causing the problem. I once had a similar experience on a Moto Guzzi. I had just put in new plugs, plus gave it a full tune up. When done it started miss firing. I checked everything again and messed with it for days. Finally after a few hundred miles I pull the plugs and put the old ones back in. Problem went away, I got a bad plug, or I damaged one when I put them in. I would start looking at things like that. Let us know what you find.


  3. #3
    Registered User
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    Dec 2007
    Reno, NV
    Double check and correct the throttle cable freeplay at the carbs. Then synchronise the carbs after at least 15 minute ride. You have a Hall sensor ignition, so don't use the "shorting" synch method you may have heard about.
    If that doesn't work, you might just have had a lousy batch of gas, as I did this weekend.

  4. #4
    Liaison 20774's Avatar
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    Sep 2005
    San Antonio, TX
    Quote Originally Posted by jforgo View Post
    You have a Hall sensor ignition, so don't use the "shorting" synch method you may have heard about.
    I don't see why not. I have a Dyna III on my /7, a hall effect system...I've shorted it before. Shorting the spark only reroutes the spark energy through the shorting mechanism to ground rather than through the plug, across the gap, then to ground. That's the important must provide a path for the energy. If you pull a spark plug cap, that's bad because the spark can't find ground.

    He has a TwinMax...that's a good tool...shorting would be something of a back up or something you might have to do on the road.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  5. #5
    Day Dreaming ... happy wanderer's Avatar
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    Mar 2010
    Vancouver, B.C. Canada
    Rummaging around desk drawers will usually produce one of these paper clamps. Bend up one of the handles to grip an old used plug. Clamp it to a cooling fin and plug in that side's plug wire. Tune your carb and check spark quality while yer at it.

    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  6. #6
    So pulled the plugs and installed the old ones, no difference. I checked the throttle and choke play and it is good and re-sync carbs after 30 min ride. While warm and runnning, sprayed choke cleaner on throttle and choke O rings on inside of carbs and idle did not change--so O rings are good. Pulled carbs off and checked the 2 small choke circuit openings on both carbs--they are open. So, button everything up and watching it idle for mins, it will be smooth, start to slow and stumble, clear up and smooth out and then start to shake again. I repalced the diaphrams last year and have not checked them now. Do they have any affect/input on idle? Since its not constant, sounds to me like fuel flow to the idle circuit is not constant?


  7. #7

    Loosen up the gas cap and see how it does

    Yah never know, I read so much about the clogged vent lines and bad gas caps. I have a co-worker with the same problem on his Triumph Speed Triple, gunked up vent lines. Go figure!

  8. #8
    Registered User Guenther's Avatar
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    Jan 2007
    Colorado Springs, CO
    I agree it looks like a fuel supply problem through the idle jet passage. But...

    A tiny tear in the diaphram?

    I would look at the timing mark when it starts shaking at idle. Just to verify that it stays solid at 'S' ... to exclude this part.

    Did you check the valve clearance again?

    Do both idle mixture screws have a nice cone shape?

    And if you are really desperate what about putting the old cables back in?


  9. #9
    Registered User lmo1131's Avatar
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    Jan 2010
    Pismo Beach, CA
    I read so much about the clogged vent lines and bad gas caps.
    Easy enough to check too. Just be careful if you crack the filler cap open at speed.
    "It is what you discover, after you know it all, that counts." _ John Wooden
    Lew Morris
    1973 R75/5 - original owner
    1963 Dnepr

  10. #10
    Registered User
    Join Date
    Feb 2005
    Deal's Gap,NC

    float Level?

    It sounds to me like one of your carbs is flooding, either from an incorrect float level, or an obstruction in the fuel inlet valve. My old '68 did this the whole 28 years I owned it. I called it "cook off", where the heat from the cylinders expanded the fuel in the bowls in hot weather when you came to a stop.

  11. #11
    Registered User Guenther's Avatar
    Join Date
    Jan 2007
    Colorado Springs, CO
    Clogged vent lines and filler cap? Negative! Jim describes the problem to be idle related and if there were a problem with vent lines or the filler cap the problem would be really showing up when riding.

    Float level could be because the main jet inlet is submerged deeper in the float bowl than the idle jet inlet. That could be checked easily by carefully removing the float bowls with the petcocks turned off. For this to be a problem the level of fuel in a removed bowl has to be really low according to my Bing diagram.

    Interesting problem!


  12. #12
    Registered User 88bmwjeff's Avatar
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    Aug 2004
    Walnut Creek, CA
    It's definitely not the filler cap. He has a 95 RT, which has the SHED system and a non-vented cap. I wonder if the SHED system is intact or if it has been removed. I doubt it's the cause if venting is not the problem, but if venting is an issue, then I would check the SHED system.
    Jeff in W.C.
    1988 R100 RT (the other woman)
    "I got my motorcycle jacket but I'm walking all the time." Joe Strummer

  13. #13
    Diaphrams are fine, put in old plugs, no difference. Checked valves and timing again, spot on ---timing mark does NOT move when idle goes into its rough state. Just for kicks, pulled the gas cap off while running and nothing changes.

    What I did find, is this is a brand new TwinMax with a new battery that I made sure was 9.5v plus. While sitting on the bike, idling and TM on top of tank bag, when the bike stumbles and gets rough, the needle on the TM will peg all the way to the left. Then I noticed that when I run it up to 3,000 rpm, needle moves to left to the 1 on dial and no matter what I do, cannot get it to adjust back. So I decided to flop lines on TM and NOW, the needle moves to the right when I increase to 3K rpm Is this normal or a problem with TM and possibly why I cant find the sync? Finally great weather here in OH and 3 days off with a poorly running RT..........

  14. #14
    Talking to Bob's bmw, the sales guy suggested that I NOT go so far on the sensitivity and to check the O rings that I just recently installed again. So I did and sure enough, I found one that was broken that I just installed. Replaced it and set the sensitivity to around 1/2 to 5/8's and that definatley made a difference in the idle. The broken O ring was on the idle mixture jet. So its probably 97% of where it was before this all started and I may just leave well enough alone. Thanks for everyone's input. Heading to Vintage Days at Mid OH tomorrow...........

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