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Thread: 1986 R80 idles too fast

  1. #1

    1986 R80 idles too fast

    My 1986 R80 has 55,000 miles on it. I bought it with 19K on it about 12 years ago. The carbs have not been touched, other than adjusted and synced twice by a professional mechanic. The last time it was synced he could not get it running quite right and suggested that I may have a diaphragm leaking. So I got two new rebuild kits to include diaphragms, new floats, float needles, new intake air tubes and new throttle cable for the right side. I did the disassembly and took all the parts to my local shop to have them cleaned in his ‘«£special bath‘«ō. I then reassembled and reinstalled them on my bike. Now it starts fine, but idles a little ruff with a small, but equal amount of gray smoke out of each exhaust. With the choke full on it idles around 2,000 RPM. As it warms up and I take the choke off the idle goes up to about 4,500 RPM and there is no more smoke. Backing off the idle adjuster screws makes no difference. If I turn them down all the way the idle increases to about 5,500 RPM. Both throttle cables have a small amount of slack in them with the throttle fully closed. As I take the slack out of the throttle grip I can feel both cables start to tighten up, so I don‘«÷t think the cables are binding. The choke cables also have a small amount of slack until tightened and when the choke lever is closed the choke mechanisms on the carbs are all the way down. I‘«÷m sure I must have done something wrong in the reassemble process, but what? I‘«÷ve got a new set of vacuum lines for syncing carbs and I plan to do this job myself also, but I need to get this idle problem taken care of first. If you have any suggestions please feel free to call or text Floyd at 636-795-9232 or

  2. #2
    Registered User 88bmwjeff's Avatar
    Join Date
    Aug 2004
    Walnut Creek, CA
    It sounds like the choke discs could be installed backwards or on the wrong side. There's a dot on the shaft of the choke disc that should be pointed forward, if memory serves me correctly.
    Jeff in W.C.
    1988 R100 RT (the other woman)
    "I got my motorcycle jacket but I'm walking all the time." Joe Strummer

  3. #3
    Liaison 20774's Avatar
    Join Date
    Sep 2005
    San Antonio, TX
    If the choke lever assembly is the issue, check Snowbum's page about 2/3 of the way down...he has pictures of all this:
    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!

  4. #4
    Registered User lkchris's Avatar
    Join Date
    Mar 2003
    Albuquerque, NM
    Check your compression.
    Kent Christensen
    '12 R1200RT, '02 R1100S, '84 R80G/S

  5. #5
    Registered User
    Join Date
    Dec 2007
    Reno, NV
    Did you dissassemble the butterflies? If you did not, and they got chemical dipped, those seals could be shot.
    Also, check if you have an air leak. Spray carb claener around the intake joints to head and carburetor. If that affects the idle, you may have found your problem.

  6. #6
    Registered User Guenther's Avatar
    Join Date
    Jan 2007
    Colorado Springs, CO
    The diaphram has a notch to line it up correctly in its seat. Happened to me once in which case the piston did not go all the way down. Which also means the jet needle is still a bit upwards and hence the higher idle. Did run fine during the test ride, though.

    You may do a quick check by removing the intake pipe and try to lift the piston with your finger and check that it comes all the way down. Better though is to remove the top cover and check the seating of the diaphram.


  7. #7
    Join Date
    Mar 2010
    Lethbridge Alberta
    If you want to check for air leaks, get a small cylinder of propane ( don't light it ) and with the bike running, open the propane cylinder slightly and pass the end around all parts of the carb & intake that you can get to. If there is an air leak the idle will increase.

    Checking the choke discs is a good idea. Also check that the pressed in top of the carb is not leaking air. They do loosen up over time and can be fixed with a light coat of epoxy on the outside. The chemical bath was not a good thing unless you stripped everything out of the carbs including the rubber O ring on the butterfly shaft. I'm not a fan of the chemical cleaners that you would use for an auto carb because they are too strong for the bings and will eat away at the finish and destroy anything that is rubber.

    Usually if an idle increases as the engine warms up then you have some kind of air leak, in effect the engine is running too lean. If it is a rich condition you'll smell the unburnt gas coming out of the tail pipe ( makes your eyes water and so on ), black/dark grey smoke. Normally the engine speed doesn't increase and you have a slower idling condition.

    You'll probably have to take the carbs off and go through them again, checking to make sure everything is in the right place. Some folks even get the portion the needle jet goes into at the base of the carb upside down.
    1995 R100Rt with Kenna Sidecar, 1998 VT1100T

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