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Thread: 1980 GS wont rev past 4000rpm

  1. #1
    Join Date
    May 2021
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    Default 1980 GS wont rev past 4000rpm

    Hello everyone!! This is my first post on this site having just picked up a 1980 550E and I am stoked to have a found such a resourceful and helpful group!!

    So the issue I am having is I am getting conflicting messages from the internet!!! (I know right!!)

    I am a marine mechanic and know my way around carbs well enough i would say and when I bought the bike the needle was stuck and the fuel was *@%^$*@%^$*@%^$*@%^$ing out when i could get it to run long enough.

    Long story short.. those carbs are a royal pain in the arse to get out with the airbox in the way but i did it and throughly checked every component long enough for my wife to wonder what the f#ck I was doing in the shop for so long!

    Now leads on to my question! I can get it run pretty nice and peppy at low rpm but when I try and punch it past 4/4500rpm it dies. I figure its leaning out and makes me wonder if the air mixture screws on top are set incorrectly. Some folks say its 2 turns out, on the sticky on this page it says 3 1/2 turns out. Which is it? I have the CV slide carbs..

    Cod this be the issue? Also makes me think it could be the timing isnt advancing..

    Anyone come across this? This bike is 4 days old for me so I'm keen to get all the bugs out before I insure it. It does already have upgraded ignition, new plugs, fresh gas and the carbs were cleaned properly with my ultrasonic cleaner, the petcock is pretty retarded but it is stock still. Probably going to be changing that!

  2. #2
    Join Date
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    Default

    If it runs sorta ok till 4000 rpm, the mixture screws are probably close - 2.5 to 3 seems typical . As you suspect, it might be leaning out thanks to a bad petcock restricting fuel delivery. Also ,when you had carbs apart, did you inspect carb diaphragms for pinholes?
    1981 gs650L

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

  3. #3
    Join Date
    May 2021
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    Yeah it runs real nice up to that 4000rpm mark. They are at 1.5 right to so I will try and see what happens and get back to the group.

    Yes, I went over all the diaphragms and they all looked good. I am also going to check the petcock just to write that off too.

  4. #4
    Nessism's Avatar
    Nessism is offline Forum LongTimer GSResource Superstar
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    Is the airbox installed?

    You might want to check over the carb rebuild tutorial linked in my signature as well as the Newbie Mistake thread so you know some thing to look out for.

  5. #5
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    May 2021
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    Yes I left the original airbox on as I have read enough on here to know that it's not worth messing with!!
    Havent had a chance to mess with the new settings yet but hopefully it will clean it up a bit.

  6. #6
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    May 2021
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    Update:

    I changed the air/fuel mixture screw to 2 turns out and it's nice and peppy once I get going. Doent have great throttle response as is but I can get up to 90km on my road pretty quickly as much as my neighbours hate it I love it!

    Idling is an absolute pain in the backside.. I hooked up my 4 vacuum gauges and its pulling 10 pounds at idle consistently but it just dies sometimes out ofb
    the blue. When I put it in gear its dies 200 rpm or so without moving. No real reason as to why and its driving a little up the wall. Good spark, good compression. Should i be checking the valves?
    Any ideas crew?!

  7. #7
    Join Date
    May 2021
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    I just let it sit for 30 mins and let it cool down.. idles like a dream, went up the road.. drives nice. Pulm into the shop to let it idle for 1 min. Stalls.. doent want to idle anymore..

  8. #8
    Join Date
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    So, how many items in the Newbie mistake thread apply to you

    So far, you haven't mentioned adjusted the valves, cleaned the carbs, or replaced any O rings
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    1970 450 Mk IIID (THUMP!)
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    1999 ATK 490ES
    1994 DR 350SES

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