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Thread: Carburation Consternation

  1. #1
    Rally Rat
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    Carburation Consternation

    Feeling rather inept right now...
    Was changing out the battery today and after getting things on the 90/6 back together
    I fired the bike up.. idled a bit rough.. I figured it was just cold, etc. and while walking
    around the bike I noticed gas flowing freely from the right side carb. I shut thigns down
    a.s.a.p.,, turned off the fuel, and it stopped. Thinking I mave have criped the cable
    when putting the tank back on I looked to see that the cable was pulling/returning
    properly (just eyeballing it) and tried again. Things were fine til I gave the throttle a
    light crack -- and the flow returned. I turned everthing off again, cleaned up my mess.
    And left it to sit until I can figure out more. My concern right now is that I accidentally loosened
    something while taking off the intake hose and it has blocked/plugged/gummed something
    up. (Though I tried to make sure the carbs were well protected/covered when doing the work.)
    Any suggestions on where to look first?

  2. #2
    rsbeemer 22600's Avatar
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    Have you checked the float?

    Usually when my carb was leaking it was because the float was stuck, not adj. properly or in the old days it was a float that was saturated. The new floats are much better.

    Take off the bowl on the right carb, then turn on the fuel tap. It should be leaking out the bottom of carb, now push up on the float. Does that stop the flow?
    If so, it's just one of the above problems.

    Of course, this shouldn't have anything to do with you changing out the battery but these things do happen.

    Let us know what you find.

    DW
    1978 R100rs MOA#22600 125cc Kymco
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.

  3. #3
    Registered User toooldtocare's Avatar
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    Stuck floats are common, my Motorsport would to that occasionally if it had not been ridden in awhile. A tap on the float bowl with a screw driver would fix it. I got tired of it after a couple of years and replaced the floats with alcohol resistant floats. My carb had the type that the floats were not attached to the float arm, but rose and sank individually. They had small pins sticking out of them that would hit the float arm to raise it. Because they had swelled they would stick in the bottom of the float bowl if the gas dried up enough to fall to the bottom. Well worth the expense, never did it again.

    Wayne

  4. #4
    Registered User helmut_head's Avatar
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    Remove the bowl and check function of the float and stop (similar to my friends above). From memory, I'm in Brazil, when I rebuilt mine I had a binding issue with that little pin/clip that couples the stop to the float arm.

    Don't somke if there is gasoline on the floor.
    Helmut always wears a Helmet.

  5. #5
    Macrunch MCrenshaw's Avatar
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    Good comments on the floats. However don't overlook the crossover fuel line that runs through the clamshell. Make sure that all fuel lines are correctly attached and clamped. Sometimes it the simple things....

  6. #6
    Registered User lmo1131's Avatar
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    ... and it may be time to replace the float needles as well.
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  7. #7
    Benchwrenching PGlaves's Avatar
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    There should be absolutely NO connection between the cable and overflowing fuel. The throttle cable controls the throttle plate which controls the flow of air. To get the proper mixture for combustion the jets control the mixing of fuel from the bowl with the air.

    But the fuel level in the bowl is controlled by the fuel floats and the fuel needle and seat. When the fuel in the bowl is at the proper level the float is supposed to press upward on the needle, pressing it against the seat and shutting off the fuel.

    So fuel overflowing from a carburetor has to be caused by one of three possibilities:

    1. Debris or something keeping the needle from closing off against the seat.
    2. A float that is out of adjustment (way out) which sets a fuel level above the overflow tube.
    3. Something preventing the float from pushing upward sufficiently on the needle. A fuel saturated float can be too heavy to float correctly.

    Since your case came on rather suddenly and dramatically I suspect issue #1.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

  8. #8
    Rally Rat
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    Quote Originally Posted by PGlaves View Post
    There should be absolutely NO connection between the cable and overflowing fuel. The throttle cable controls the throttle plate which controls the flow of air. To get the proper mixture for combustion the jets control the mixing of fuel from the bowl with the air.

    But the fuel level in the bowl is controlled by the fuel floats and the fuel needle and seat. When the fuel in the bowl is at the proper level the float is supposed to press upward on the needle, pressing it against the seat and shutting off the fuel.

    So fuel overflowing from a carburetor has to be caused by one of three possibilities:

    1. Debris or something keeping the needle from closing off against the seat.
    2. A float that is out of adjustment (way out) which sets a fuel level above the overflow tube.
    3. Something preventing the float from pushing upward sufficiently on the needle. A fuel saturated float can be too heavy to float correctly.

    Since your case came on rather suddenly and dramatically I suspect issue #1.
    Thanks to everyone for all the help

    So far it appears to be #1.
    I had only a brief time to look into this afternoon. I removed the bowl - yes there were a couple small partcles of something in the bottom - turned to mush when I went to wipe them out. I then opened the petcock and fuel began to flow. I lightly lifted the floats and while it did slow to a trickle, it did not stop completely. Figured it was not in the best interest to see what pressure it took to make it fully stop. I will get a chance Tuesday to go back in and take a closer look. At this point do I a) let fuel flow through the assembly to flush out any foreign objects? or b) get a can of carb cleaner and "spray wash" the area? or c) ???

    As far as smoking... first - it's not allowed in garage. 2nd - FULLY understood. It took forever to clear the fumes after the inital flow-over on Saturday.

  9. #9
    Douglas Williams
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    With the bowl off, try lifting the float until the fuel stops flowing even if it's past parallel. If the fuel stops, adjust your float level. If it doesn't, remove the carb and try some carb cleaner, compressed air and perhaps even a fine wire to clean the jet. Be careful removing the float as one end of the pivot rod is knurled and pushing it out the wrong way could damage or break the mount. Hopefully, it's just an adjustment problem. If you're able to stop the flow by raising the float manually but it still leaks after adjustment, you may be buying new floats. IMO.
    Doug
    Sent from a Galaxy, far, far away

  10. #10
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    Update!

    Finally had the chance to dive back in... tried the manual raise float until the gas stops test... still just a trickle making it through... noticed the needle valve was not dropping down when the floats were lowered. A quick shot of carb cleaner loosened it, but it was still sticky/slow to drop, and still allowed a trickle during the test. I pulled the pin, lowered the back of the floats and pulled out the needle valve. the ball bearing at the top was "gritty" as I tried to roll it around. Gave it a quick bath in cleaner -- rolled much smoother. Reinstalled the pin, re-set the float (everything smooth there), turned on the fuel -- flowing much more freely now -- lifted the floats... and it comes to a complete stop. Put float bowl back together, turned on fuel. NO OVERFLOW!

    At this point I was very happy.

    Started the bike, had to bring the throttle wide-open before it would take off... and after bringing things down it dies, no low idle at all.

    Was my needle valve just an indicator of grit/grime elsewhere?

    Here's where I seek advise from the group.
    As I learn more about the carburatoion process -- what areas do I look at/clean next?

  11. #11
    Benchwrenching PGlaves's Avatar
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    It seems you have debris of some sort in the fuel which is fouling the carburetor in more than one location. You need to do two things:

    1. Eliminate the source of the crud in the fuel. Remove the tank and thoroughly clean out the fuel tank. I would remove the petcocks to do this. Then, make sure the fuel lines are sound and not shedding rubber bits. Clean the screens. I would install in-line fuel filters. Use filters that are big enough to fully flow the fuel the engine needs; not itty bitty filters.

    2. Use spray carb cleaner and compressed air to clean the jets and passages. Remove and cneck/clean the jets. Don't mix parts - do one carb at a time.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

  12. #12
    Stage Crew beemerPhil's Avatar
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    I suspect a bit of crud has found its way into one of your pilot jets- the smallest brass screw inside the float chamber. Pull the jet, examine and clear it, and replace it. Use a new o-ring with a bit of motor oil on it so its seats smoothly.

    A likely source of debris in the fuel path is decaying fuel lines. BMWs fuel line, with the braided wrapping, will look brand new long after the insides have begun to deteriorate, esp. with the use of ethanol fuels. My guess is that the particles you described are just that; bits of fuel line dissolved by the ethanol, and dislodged when you moved the fuel lines while removing/reinstalling the tank. There are filter screens on the petcocks; not much gets through from the tank. Replace the fuel lines and clean the existing debris from the bowls and jets, and you should be good to go.
    Phil Keppelman #20331
    MOA Rally Stage Manager
    The shortest distance between two points.............
    ain't how I got here......

  13. #13
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    Quote Originally Posted by beemerPhil View Post
    I suspect a bit of crud has found its way into one of your pilot jets- the smallest brass screw inside the float chamber. Pull the jet, examine and clear it, and replace it. Use a new o-ring with a bit of motor oil on it so its seats smoothly.

    A likely source of debris in the fuel path is decaying fuel lines. BMWs fuel line, with the braided wrapping, will look brand new long after the insides have begun to deteriorate, esp. with the use of ethanol fuels. My guess is that the particles you described are just that; bits of fuel line dissolved by the ethanol, and dislodged when you moved the fuel lines while removing/reinstalling the tank. There are filter screens on the petcocks; not much gets through from the tank. Replace the fuel lines and clean the existing debris from the bowls and jets, and you should be good to go.
    With my son's High School graduation and party over, I was *FINALLY able to sit down and dedicate some time to the machine. Pulled the right hand carb (the one with the blac bits in the bowl) and gave it a good cleaning with carb cleaner and some compressed air (also spray around the left carb, since I was going). Replaced the fuel line and it looks like I may be ready for "Ride To Work" day on Monday!!! Thanks for all the help and advice

  14. #14
    Registered User lmo1131's Avatar
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    Pulled the right hand carb (the one with the blac bits in the bowl) and gave it a good cleaning with carb cleaner and some compressed air
    And while you were at it you pulled the LEFT hand carb and did the same thing.. .. . .. r i g h t ?

    And

    Eliminate the source of the crud in the fuel. Remove the tank and thoroughly clean out the fuel tank. I would remove the petcocks to do this. Then, make sure the fuel lines are sound and not shedding rubber bits. Clean the screens. I would install in-line fuel filters.
    If you had to maintain full throttle of even get it to run, you've got a clogged main jet... at least that's what I found when my /5 acted the same way. FWIW.
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

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