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Carb help!!

Discussion in 'All Terrain Vehicles' started by jab08, Sep 22, 2011.

  1. Sep 22, 2011 at 10:49 AM
    #1
    jab08

    jab08 [OP] Well-Known Member

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    I need some help!! I have a 2002 yamaha big bear 400. It has a mikuni carb on it. Its been sitting for about a year and I'm trying to get it running. Iv cleaned out the jets and the bowl. What I'm running into is that it will not run but if you put you hand over the intake it will start right up and idle. I'm not sure what the problem is? Tuning or does the carb need rebuilding?? Thanks for the help and sorry if it don't make sense I'm typing on my phone.
     
  2. Sep 22, 2011 at 12:31 PM
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    jab08

    jab08 [OP] Well-Known Member

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    Any clues??
     
  3. Sep 22, 2011 at 12:36 PM
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    Bloodhound

    Bloodhound Space For Rent

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    From my experience when the float needle (I can't remember what it's called exactly right now) under the floats is gummed up the motor will start and run with full choke on. I'd pull it apart and clean out all the jets also. Try to avoid moving the air screw though, or turn it in and count how far it was backed out before anything else.

    edit: just read you've cleaned all the jets, I'd look at the float seats again.
     
  4. Sep 22, 2011 at 12:46 PM
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    jab08

    jab08 [OP] Well-Known Member

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    Ok thanks man! I just took it completely off so I can clean it real good. Hope it fixes it.
     
  5. Sep 22, 2011 at 8:13 PM
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    Bloodhound

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    Any luck with that? I'm hoping after you get it back together it should run just fine.
     
  6. Sep 25, 2011 at 2:49 PM
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    medic2230

    medic2230 Ditch Doctor

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    Are you blowing everything out with an air compressor after you clean it? If there is any small amount of trash in there it will cause problems. Ask me how I know. :)
     
  7. Sep 25, 2011 at 3:11 PM
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    jab08

    jab08 [OP] Well-Known Member

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    Thanks everyone!! But I took it apart and let it soak in some cleaner, just haven't had time to put it back together. But good tip on using an air comp. Before I put it all back together. I'll keep you all updated.
     
  8. Sep 25, 2011 at 3:14 PM
    #8
    ktmrider

    ktmrider Senior Member

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    Ive rebuilt so many carbs and that float and the pin needs to be perfectly free of varnish and gum to get it to run without the choke. what I usually do is get a big can fill it with paint thinner and then let the entire carb soak and then take a tooth brush pick or whatever and work on it until everything is smooth. When you stop riding it again make sure to empty the carb and put fuel stabilizer in the bike or empty the tank.
     
  9. Sep 25, 2011 at 3:20 PM
    #9
    YFZ450MOE

    YFZ450MOE When you blow off steam you get an eyepatch

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    1. The needle that is connected to the float and the carb on the pivot end is stuck closed.

    2. The air fuel mixture is not right. Could be due to the screw missing or out of adjustment. Having the screw out would make it to rich or if it's tofar in then to lean. The screw is on the bottom of the carb and as for a yamah keihn It carb should be a very small flat head to adjust. Screw it all the way in then out 2 full turns. See if it runs. If not proceed to a turn a half turn again and check.

    3. Could also be improper jetting. Has there been any motor work, intake work, exhaust or anything done to it. If so it may need to be rejetted. Does it have an air box lid?
     
  10. Sep 25, 2011 at 3:39 PM
    #10
    jab08

    jab08 [OP] Well-Known Member

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    Thats exactly what I was about to ask about how many turns on the screw. I counted but just was wondering. But its completely stock.
     
  11. Sep 25, 2011 at 5:00 PM
    #11
    YFZ450MOE

    YFZ450MOE When you blow off steam you get an eyepatch

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    If it's completely stock clean your filter and put the air lid box back on. Turn the screw in all the way but just snug. To tight it will snap off. Then go out 2 turns. See how she runs, if it's like shot then go out a quarter to a half more. Then repeat till you get what you want and it sounds good. Run it through the entire RPM range and when ya get it close there won't be any pop on the deceleration of the engine. Let me know what ya get!
     
  12. Sep 25, 2011 at 5:52 PM
    #12
    jab08

    jab08 [OP] Well-Known Member

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    Ok thanks!! I hope to get it running in the next few days.
     
  13. Sep 27, 2011 at 9:23 AM
    #13
    jab08

    jab08 [OP] Well-Known Member

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    Ok I think Im getting close!! My friend put it back together for me and said it runs fine but its popping through the intake during deceleration. Does that mean that its running to rich or to lean??
     
  14. Sep 27, 2011 at 9:29 AM
    #14
    jab08

    jab08 [OP] Well-Known Member

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    Thanks!! I just picked up 2 new plugs just in case I foul them out before I get the correct tune. How much should I look at turning the screw to rich it up? 1/8 to a 1/4 turn maybe?
     
  15. Sep 27, 2011 at 12:11 PM
    #15
    jab08

    jab08 [OP] Well-Known Member

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    Ok well it will not idle for very long without popping then cutting off. I put in a new plug and keep letting out a 1/4 turn wich should rich it up correct? However I keep checking the plug and the tip is getting white which means its still running lean correct? Should I keep adjusting the screw or what should I do?
     
  16. Sep 27, 2011 at 12:55 PM
    #16
    jab08

    jab08 [OP] Well-Known Member

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    I think it only has a idle gas screw. At least I think. That and the high and low speed jets is all that I see on the carb.
     
  17. Sep 27, 2011 at 1:32 PM
    #17
    jab08

    jab08 [OP] Well-Known Member

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    Yes very true lol!! How would I determin which one it is?
     
  18. Sep 27, 2011 at 4:35 PM
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    YFZ450MOE

    YFZ450MOE When you blow off steam you get an eyepatch

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    Popping on the decel is to lean. so yes, correct. Keep turning out the screw a 1/4 turn at a time, if you get to the end of the screw when its to loose and won't stay where it should then, go up one on the pilot jet. Then start it all over again, screw all the way in, then out 2, then a 1'4 turn at a time. Having your plug look like a brown paper sac is what your aiming for!
     
  19. Sep 27, 2011 at 5:07 PM
    #19
    WTtoolman

    WTtoolman Facial bones colapse as I crack your skull in half

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    Your quad has a fuel screw and idle adjuster. 2.5 to 3 full turns out on the fuel screw for those yamahas is ideal. Did you make sure the jets were completely clean? Could you see daylight through them? When you re-installed fuel screw, was there a spring, a washer and a tiny o-ring? You also need to blow air through the carb where the jets screw in to make sure all the internal passages are completely clear. If you have anymore problems PM me, I do this for a living.
     
  20. Sep 27, 2011 at 7:35 PM
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    jab08

    jab08 [OP] Well-Known Member

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    It is running way too lean and Iv about got the screw all the way out. YFZ450MO when you say go up one on the pilot jet what exactly do you mean? 1 turn in or out? And WTtoolman all the jets are spotless I have cleaned them like 4 times already and yes the fuel screw had a spring and a washer cant clearly remember if it had a o-ring though.
     
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