thumper carb question...idles and runs but..

Discussion in 'The Garage' started by jlbpa, May 12, 2013.

  1. jlbpa

    jlbpa Adventurer

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    Aug 5, 2006
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    41
    honda xr80r. Finally got the fuel system cleaned out and it idles and runs but bogs down when I give it gas. I think it's getting too much gas. I think everything in the carb is clean I'm wondering if it's time to try adjusting the float. But this begs the question....how does a float get out of adjustment?
    #1
  2. disston

    disston ShadeTreeExpert

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    Floats can take on gas which makes them heavy. If they are metal, usually brass, they can get pin holes in them that gas gets into the float. You can sometimes, but not always, detect the gas inside the float by shaking it. This is not a definitive test because the amount of gas is small and may not have enough mass to make a determinable sloshing sound or some other indication. Same thing happens with plastic and Styrofoam floats. The extra gas makes them heavy. The heavy float lets more gas into the bowl.

    If the floats are available it's worth the try. I don't know about those carbs in particular. If there are sliding needles they can wear and the jets the needles are in may be worn. Sometimes slides get worn. Look for signs of wear on moving parts. However the deminsions of carb parts are so critical that wear is not visible with the naked eye. It may be that realizing a part wears is the only indication you get that it is worn. Have to go by the fact it has X number of miles, time to refresh, rebuild.

    New floats usually get new float needles also. They work together. SOP
    #2
  3. joexr

    joexr Banned

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    Try taking the airbox boot off the back of the carb. If it's better , you're right it's rich. If it's worse , try partially obstructing the intake with a rag , which will make it richer. I think you're lean though.
    #3
  4. ttpete

    ttpete Rectum Non Bustibus

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    What does the air filter look like? It could be dirty or deteriorated or there could be a mouse nest in the airbox.
    #4
  5. freetors

    freetors Been here awhile

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    In the case of metal floats, if they do have pinholes you can carefully solder them closed. If it's some other material just buy new floats.
    #5
  6. wmako

    wmako bored in NJ

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    Usually with these little bikes, it is the opposite problem, not getting enough gas. They are very lean from the factory to begin with, and if the holes in the carb get even a little dirty, they won't run well.

    Have you looked at the spark plug after it stalls when you try to open the throttle? Have you let it get fully warmed up? Have you tried running with the choke partially closed? What happens if you try to roll the throttle on very slowly?
    #6
  7. Dr. John

    Dr. John Adventurer

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    A friend of mine had a small ( 50/75/80 ) Honda that his son rode,and had a similar problem. It turned out to be that either the needle,or needle jet had worn enough to give the same symptoms you describe. As I remember it was an old Honda service manager that saved him from buying a new carb.
    #7
  8. qkenf4u

    qkenf4u Been here awhile

    Joined:
    Jul 25, 2009
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    nice warm bike riding COTTONWOOD ARIZONA...
    could be as simple as water in the gas... the garbage we call gas today sucks water out of the air like crazy (ethonal is garbage)....

    huge huge problem here at my shop in AZ.
    #8