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Thread: 84 big red carb issue

  1. #1
    Join Date
    Apr 2010
    Location
    pa/washington county
    --
    20

    84 big red carb issue

    my big red has a carb issue.i have rebuilt it including changing the slide tube pressed in the carb body. my needle is on the middle knotch where it should be.the mixture screw is 1.5 turns out and i still have a dead spot in the throttle.jetting is stock has a uni filter and stock exhaust. if i ride it and get on it it bogs but if i pull the choke up some it takes off. do it need a larger main jet ? kinda stumped here.

  2. #2
    Join Date
    Mar 2010
    Location
    Pacific NW
    --
    4,255
    More than likely a plugged slow jeyt
    They'll stumble off idle.
    An .008" or .010" guitar string should fit thru the crud
    but they say to never use wire to clean them.
    Exhaust seems to affect the mix/jetting more than air filter IMO
    Attached Thumbnails Attached Thumbnails JETgraph.jpg  

  3. #3
    Join Date
    Apr 2010
    Location
    pa/washington county
    --
    20
    I just cleaned. The carb throughout.completely apart n all was spotless.still has me stumped

  4. #4
    Join Date
    Mar 2010
    Location
    Pacific NW
    --
    4,255
    Quote Originally Posted by paul kondratiuk View Post
    I just cleaned. The carb throughout.completely apart n all was spotless.still has me stumped
    so you can see thru the slow jet?
    Just because the jets are clean, doesn't mean the internal passages are.

    I can only say this because I've missed stuff and have done everything wrong
    at least once.
    Be happy it's not a 250 carb. Those take forever just to get on and off.

    so?
    you pressed in a new main needle jet? Was your old one wallered out?
    Did it look the same ?
    What is the rebuild kit name?
    I had 2 identical kits same part numbers, for instance, and the float needles were different lengths.

    Did it ever run that you heard?
    is it new to you?

    It will still run if you give it a little choke?
    Gas tank vent ok?

    man, I'm trying to get someone else to chime in.

    Worst case, is replacement carbs are like 20 bucks.
    Vacuum leak?...spray something around the carb mounting surfaces while it running and see if it changes.

    Valve adjustment close? That'll throw off the timing.
    Let's see, that else.

    so it stumbles off idle but will run up ok?
    I've ruined new plugs within minutes of crappy running.

    You'll get it. We always do.

    Bottom line, it sounds lean.?
    Does it backfire?

  5. #5
    Join Date
    Apr 2010
    Location
    pa/washington county
    --
    20
    It doesnt backfire,idles normal .if i take off easy it pulls great but if i drop the while riding along it just falls face down.i have exhausted my options here.valves are right,cam chain is in adjustment too.i purchased a replacement carb n tried to tune it also,was worse than The stock one

  6. #6
    Join Date
    Oct 2010
    Location
    Tucson
    --
    1,652
    Did you check your gas flow coming out of the tank? Filter inside the tank?

  7. #7
    Join Date
    Apr 2010
    Location
    pa/washington county
    --
    20
    I have a plastic replacement tank.oem petcock n inline filter full of fuel.

  8. #8
    Join Date
    Mar 2010
    Location
    Pacific NW
    --
    4,255
    Quote Originally Posted by paul kondratiuk View Post
    I have a plastic replacement tank.oem petcock n inline filter full of fuel.
    I bought a clear fuel filter with a paper element that would NOT let gas thru except a drip at a time.

    Man, I wish I knew what to tell you.
    Mouse nest in muffler?
    Air filters can sometimes need to be correct because they can add resistance
    and kinda richen the mixture but they should haul &^% without one.

    Lean usually backfires, or headpipe glows red.
    I'm at a loss.

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