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Discussion Starter #1
Hi,
2 questions.
The easy one: does anyone have an electronic copy of a 2007 bigbear 250 service manual?
The harder one: I also have a 2003 Kodiak YFM400FA and is running rich. Bar taking the carb apart to see if anything wrong in there (which I only want to do at last resort...), is there anything I can try, adjust, fiddle with to solve the pb? I'm not keen taking the carb apart simply because I need the bike for work, so don't want to risk it out of service for too long.
Tx
 

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Assuming all else in the carb is ok, if its running rich its a jetting problem. carb's got to come apart to rejet.
without more information impossible to diagnose. are you saying its rich because of spark plug color? is it loading up? when is it loading up, low speed rpm's or through the entire throttle range?
 

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did you have any thing done too it? becuase i bought mine new in 03 and left it alone and had great luck with it ever since
 

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Discussion Starter #5
You're very right. I bought the Kodiak second hand and I suspect previous owner had fiddled too much with it :(, and have lots of problems with it. I bought the big bear new at the same time, never did anything to it and it runs like clockwork...
did you have any thing done too it? becuase i bought mine new in 03 and left it alone and had great luck with it ever since
 

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Discussion Starter #6
Thanks for the answer.Taking the carb apart... I was afraid that would be the case...
Not sure what you mean by loading up, sorry. Exact symptoms are: plug very black, black smoke at all rpms but esp when revving up or at high rev, and when hot tends to stall and then hard to start again (feeling flooded because when starting again sputters and doesn't hold idle well for awhile). Oddly but I'm not sure it's related the carb drain seems a bit wet some times - I haven't caught any actual fuel draining but it's not completely dry.

Apart from taking carb apart (which I'll probably have to bite the bullet and do), can anything help like improving air intake ? (can you tell I'm not keen on the carb work...:) ?)

Assuming all else in the carb is ok, if its running rich its a jetting problem. carb's got to come apart to rejet.
without more information impossible to diagnose. are you saying its rich because of spark plug color? is it loading up? when is it loading up, low speed rpm's or through the entire throttle range?
 

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Loading up = indications of too much fuel, not really flooding but gurgling like its fuel rich. And since you did post symptoms it sounds like the case. However having a little fuel in the bowl drain tube may indicate another issue entirely. So you might have two problems, and though not really related, one can still affect the other.
First thing you need to do, is find out what stock jetting is for that model. Both main jet number and pilot jet number, then when you open the carb up you can compare and see if the jets have in fact been changed. (bigger numbers = bigger openings in the jets)
I suspect because of the dribbleing fuel issue, you may have some crud in the fuel tank thats making it to the carb. Just one little speck of dirt stuck in the needle/seat will prevent the float from closing entirely and allowing gas to continue to flow into the bowl. I have seen in some cases where gas would flow back through the carb into the air box, that condition in itself would cause it to run rich and create the issues you mention.
A simple diagnosis would be to pull the lid off the airbox (leave the filter in place) start and run it and see if there is any improvement.
Find the spec's on the carb, not only jet sizes but float level as well, and order a complete carb kit. disassemble the carb completely, not forgetting to count the number of turns out the pilot screw and idle screw are. (Turn the screws in til seated lightly counting the number of turns it takes to seat them) clean the carb well with carb cleaner and blow out all passages with compressed air. Install a new needle and seat, being careful not to damage the o-ring that seals the seat in the carb body. (hint here, i always dab a bit of white grease on carb o-rings) new o-ring in the main jet holder and new o-rings on the pilot air screw and idle adjustment screw. note that both the pilot and idle adjustment screws both have a spring, then small washer and o-ring on them so dont lose any of these small parts during disassembly or assembly. (remember to screw both the pilot screw in until lightly seated, and back out the same number of turns you counted during disassembly)
After the new seat is installed, hook the needle on the tab on the float and with the needle/float in place install the float pivot rod.
Generally speaking float height is measured with the carb top inverted, gasket removed, and measure with a caliper from the gasket surface (gasket removed) to the highest point on the float. Then to adjust if necessary remove the float from the carb and bend the little tab the needle hangs on, slightly to raise or lower the float level.
Remember, since the carb is inverted, the larger the measurement, the lower the float level is. I generally set a float level about a mm lower than specs and have had no issues doing so.
before hooking up the fuel line from tank to the carb run a little gas out into a jar and look closely for any garbage in the tank, you may need to pull the fuel tank and flush it. My method of doing this is with the tank fuel cap and fuel petcock removed, is a garden hose and spray nozzle. stick the nozzle in the tank and move it around to spray all areas inside the tank, dump the water from the tank and repeat 2 or 3 times. turn the tank upside down and let it drain for a half hour or so. While the tank is drying inspect the screens on the fuel petcock and clean if necessary. plug the fuel petcock hole in the tank with your finger and dump in a bottle of rubbing alcohol, put the cap on the tank and shake it around, open the tank up and dump it out. The alcohol will remove any remaining water. blow the tank out with compressed air and reinstall. Note, be sure to install a quality fuel filter in the line before attaching the line to the carb.
 

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Discussion Starter #8
:tup: :)) :tup:
Brilliant, thanks a million. I suspect you're right with the tank dirt, given the amount of hard farm work this machine does, there is a lot of dust/debris/seeds floating in the air, including s/times when refuelling.
Now just have to roll up the sleeves and tackle the carb. Fingers crossed.
Thanks a lot.
 
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