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Thread: 1983 GS550ES Revs out of control when it gets hot

  1. #1
    Join Date
    Feb 2021
    Columbus, Ohio

    Default 1983 GS550ES Revs out of control when it gets hot

    Hi All,

    This is an extension of my previous forum post but since that was in the fuel delivery section I figured I would start a new thread here. Here is a link to the previous thread for any who want to read about this disaster of a motorcycle and what we have tried on it.

    So basically Chris and RPhillips were right in that the size 40 pilots were not the issue on this. I replaced them and tried adjusting the idle stop screw and I also tried adjusting the air fuel mixture screws, but whenever this bike gets really hot it revs out of control to 5k and beyond. The hotter it gets the higher it revs essentially. I thought I would do another check for a vacuum leak and this time instead of a propane torch I used a fog machine to see if I could see any smoke coming out of the exhaust but there was nothing. No change in idle or noise and I couldn't see anything being sucked in. When the bike was only slightly warm i took it for a ride thinking i fixed the problem after replacing the jets and it was really having a hard time getting any power in the 1-4K rpm range until it warmed up. This was with the 35 pilot jets and the factory 2.5 turns on the air fuel screw. I really do not think this is an issue with the carbs at this point because it runs the exact same with the 40s as it does with the 35s. Is there anything in the timing i should maybe check? I was reading about a guy with a 93 Ducati who had the same problem and someone mention ignition advance causing this issue. Again I'm grasping at straws here as usual but this makes no sense why it should not be running. Thanks for all the help in advance.


    PS:gs550es.jpg picture attached of bike

  2. #2
    Join Date
    Feb 2018
    oregon city, Or.


    Where are you looking for vac leaks??? At the base of intake manifolds? I've seen that before, or if they get severe cracks...
    '82 & '83 GS1100e

  3. #3
    Nessism's Avatar
    Nessism is offline Forum LongTimer GSResource Superstar
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    Join Date
    Mar 2006
    Torrance, CA


    The ignition advance is built into the ignitor. Those boxes typically either work or not. It's rare for the ignitor to malfunction.

  4. #4
    Join Date
    Aug 2010


    Have you replaced the o-rings p/n 23 at head/manifold interface?
    1981 gs650L

    "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

  5. #5
    Join Date
    Jul 2021
    West London


    Speaking generally - if it happens as it gets hotter it would suggest a weak mixture/ air leak or throttle not closing. Did you check for play/wear in the throttle shafts - become unreliable in closing and get worse as carbs heat up, also let air in? Ive seen this on old CV carbs on cars. Just a thought

    (I had similar symptoms and found carbs out of balance and 1 badly leaking manifold. Gave the carbs a good clean up & balanced, siliconed the manifold and problem fixed)

  6. #6
    Join Date
    Mar 2016
    Toronto Ontario


    Revert carbs to stock
    Replace internal seals. Robert barr has good cost effective stuff.
    Replace manifold seals. Robert barr has good cost effective stuff.
    Set valves to spec.
    Report results
    It worked in Hammamatsu return to the egg. These were the poor child of their class there was little available to make one suspect there are any exotic internals thwarting you.
    Propane? smoke machine? Hmmmmm. No mirrors? Borders on the whore in a fit method of coping with a problem.
    1983 GS 550 LD
    2009 BMW K1300s

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