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Thread: 1983 GS550ES Fuel Delivery Issue

  1. #1
    Join Date
    Feb 2021
    Location
    Columbus, Ohio
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    27

    Default 1983 GS550ES Fuel Delivery Issue

    Hi All,

    Im not even sure what to list this as so I just put it here.

    So basically I have an 83 GS550ES that looks like it just rolled off the showroom floor because it was kept in a guys living room for 30 years but under all the glamour this thing has some sort of serious air fuel mixture problem that I can not figure out. I thought It was the intake o-rings but I replaced those to no avail (they were very flat though). The main problem is that when its running it will idle around 1100 rpm at start and then slowly rise to about 2000 and then if you give it any amount of throttle it will immediately rocket up to 5000 rpm and never come back down.

    A list of things we have tried:

    -Cleaning the carbs
    -confirming correct jet size
    -made sure all the vacuum lines are in good order and in the correct place
    -checked the float bowl level
    -checked the slides to make sure they fall at the same time
    -greased the boots at the airbox to carb boots
    -I used WD40 on all boots when installing to make a good seal
    -replaced boot clamps
    -checked diaphragms on the carbs
    -cleaned fuel pet cock and ensured it was delivering adequate fuel and the vacuum was pulling fuel from the petcock in ON and RES positions
    -checked coil packs to make sure they spark the plugs
    -new spark plugs (correctly gapped)
    -New battery
    -went over the carbs like 4 times.

    The last thing I did one it was check the fuel petcock filter to make sure it was clean and I just tried starting it after priming the carbs with fuel and putting it in the RES position (only 1 gal of gas in tank) and the damn thing wont even start now. It just cranks and cranks and cranks. Am I missing something thats stupidly obvious here? or is this just the bike from hell??

    Anyways sorry for the rant and long post I appreciate your guy's help in advance.

    Thanks,
    Joe

  2. #2
    Join Date
    Aug 2010
    Location
    Sebago,Maine
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    Default

    “It’s running it will idle around 1100 rpm at start and then slowly rise to about 2000 and then if you give it any amount of throttle it will immediately rocket up to 5000 rpm and never come back down.”

    these things are sensitive to “choke” position . Once bike is sorta warmed up ,you need to keep backing “choke” off or it will race just like you’re describing...especially with throttle applied.

    You have done lots of work......but I would have replaced the o-rings at carb boot/ head interface.

    1981 gs650L

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

  3. #3
    Join Date
    Jun 2018
    Location
    Mifflinburg, PA / Land of Tar & Chip
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    2,642

    Default

    What do you mean by “all the vacuum lines”? There is only one. From the front of carb 2 to the smaller or the 2 nipples on the petcock.

  4. #4
    Join Date
    Jul 2015
    Location
    Switzerland
    Posts
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    Default

    Those are VM carbs? Then it could be that the "butterfly" part connecting the throttle cables to the combined throttle shaft came loose (It's what happened to me).

    If it doesn't start at all however, then there must be a different issue.

    Try dropping down a teaspoon of gasoline down each cylinder (through spark plug hole). If you get it to fire, your problem is with fuel/air mixture/delivery. If not, it's spark/electrics.

    Tackle one issue at a time.

    Just because it looks pristine, doesn't mean it has more than a few issues common to bikes of this age.
    #1: 1979 GS 550 EC "Red" – Very first Bike / Overhaul thread        New here? ☛ Read the Top 10 Newbie mistakes thread
    #2: 1978 GS 550 EC "Blue" – Can't make it a donor / "Rebuild" thread     Manuals (and much more): See Cliff's homepage here
    #3: 2014 Moto Guzzi V7 II Racer – One needs a runner while wrenching

  5. #5
    Join Date
    Feb 2021
    Location
    Columbus, Ohio
    Posts
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    Default

    I guess shouldnt have said vacuum lines what I meant was i connected the one vacuum line from the petcock to the carb and then i connected the two lines that vent the carbs to atmosphere, plus the fuel line itself

  6. #6
    Join Date
    Feb 2021
    Location
    Columbus, Ohio
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    Default

    Hi Roeme,

    Im not sure what a VM carb is but looking it up looks like youre talking about the single barrel carbs. These are the Dual Barrel carbs for the 572cc engine for an 83 gs550es. Not sure what the problem is but i threw a clear vinyl fuel line on yesterday to check fuel flow and it doesnt pull any fuel on the On/Res positions with the vacuum line connected, and when i try to use prime it doesnt send fuel through like it should. I checked the petcock and it is very hard to turn but it looks like the valve inside works correctly and the piece the vacuum operates on looks like it goes back and forth ok. I think its getting a serious lack of fuel for some reason. I only have around a gallonish of fuel in there so maybe its just low on gas and prime wont work? anyways thanks for your help.

    -Joe

  7. #7
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    Feb 2021
    Location
    Columbus, Ohio
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    Hi Tom,

    Like i said in the post above I did just replace the O-Rings at the intake because i thought that was the problem but it isnt. Im pretty sure the choke is working because when i had the carbs apart i could see it moving back and forth when i was using the choke lever. Is there anyway to check to see if the chokes are getting stuck in the choke port in the carb while they are installed? Again i have tried running it with the choke on/off and it was running like i described with the choke completely off. Thanks again

    -Joe

  8. #8
    Join Date
    Aug 2010
    Location
    Sebago,Maine
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    Ok, it was early and I missed the o-ring replacement....

    “and when i try to use prime it doesnt send fuel through like it should.”

    add some more gas.....if it still doesn’t flow in “PR” ,get a new petcock - don’t waste your time fiddling with or admiring a 40 yearold petcock . Measure bolt centerline spacing on petcock..lots use a 44mm spacing. Determine whether you must have petcock outlets facing towards front or if there’s room to face them back, cuz later is more typical.
    Understand that this cold start system is an enricher,not a “choke”....it sends an extra dose of fuel into carbs throats to aid starting . Do not use any throttle during “choke” application or you defeat its purpose.
    1981 gs650L

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

  9. #9
    Join Date
    Jun 2005
    Location
    Norene TN
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    There should be a very fine filter attached to the pet cock, inside the tank, check to be sure it isn't clogged. Even with a non working pet cock, it should be wide open when in PRI position. Just my opinion.
    1983 GS1100E, 1983 CB1100F, 1991 GSX1100G, 1996 Kaw. ZL600 Eliminator, 1999 Bandit 1200S, 2005 Bandit 1200S, 2000 Kaw. ZRX 1100

  10. #10
    Join Date
    Mar 2016
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    Toronto Ontario
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    Quote Originally Posted by rphillips View Post
    There should be a very fine filter attached to the pet cock, inside the tank, check to be sure it isn't clogged. Even with a non working pet cock, it should be wide open when in PRI position. Just my opinion.

    Yes wide open on prime.
    Disconnect the fuel line from the carb and fuel should flow on prime.
    If it does then it should also flow if you suck on the vacuum line whilst it is in the other 2 positions.

    If you have fuel flowing from the petcock reconnect the line to carb and remove the float bowl drains. Fuel should flow from these if all is well.
    There are tiny dome shaped filters attached to the float valve seats but I had mine apart after 30 odd years and they were clean as a whistle. These are a royal pain in the ass to get out without damaging them so as long as fuel will come out of the bowl drains do not bother.

    So two things to check in the fuel flows path.
    Confirm these and we can move on.

    Tom from Maine was right about the choke position. The bike will warm up quickly and you will get a rapid rise in RPM so you have to drop the choke back incrementally during the warm up. But thats not an issue now go check for fuel flowing.

    I once had a gelationous and semi varnish buildup inside the petcock which required it be dismatled and cleaned.
    You cracked open the carbs and did farm more difficult things so if you get no flow its worth a check.


    Also remove the gas cap when your doing this.
    Last edited by Cipher; 04-28-2021 at 05:52 PM.
    1983 GS 550 LD
    2009 BMW K1300s

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