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2000 Yamaha Bear Tracker 250 Choke Plunger Backward??

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I have a 2000 Yamaha Bear Tracker 250 (YFM250) which starts up right away and runs ok for a bit, but with less than 1/2 the power of my other Yamaha Bear Tracker. Eventually after riding, it blackens the spark plug and runs awful and eventually doesn't want to start or run at all.

CHOKE ISSUE: When you Pull the Choke Plunger 100% OUT, the idle goes DOWN....then pushed in at 1/2 position the idle goes UP and Choke Plunger pushed ALL THE WAY IN...Idle goes up even higher...? It acts like the plunger action is backward from our other 2004 Yamaha Bear Tracker (which idle goes up when pulling out, like normal).

---} Choke OUT = Normal Idle

--} Choke IN 1/2 WAY = Higher Idle

-} Choke IN FULLY = Super High Idle

(For this reason, it has to run with the choke position all the way OUT or else it idles high and dies when you try to give it throttle.)

While running it has very little power compared to our other Bear Tracker regardless of RPM. Less than half of the power, in fact.


1. Replaced Full Intake Boot Assembly From Carb-to-Head

2. Replaced Spark Plug

3. Replaced Ignition Coil and Spark Plug Wire

4. Replaced Air Filter


Any and all help is greatly appreciated.


Thank you!


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That sounds to me  like it  is running too  lean at  idle.  Try  setting the  idle  down  to  normal  with the  choke in and then  work  from there.  You  may  find  you  have to  readjust the  idle  air  screw a  bit  richer  when  you  do  that ..   At speed  I  think  you  are  losing power and fouling the  plug  because it  is running way  too rich  when  off   idle and warm.

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UPDATE: (Not Solved) Ok... Took your advice and set the idle screw to idle properly at "Choke IN" Position now, so it idles properly when the choke is in (Idle still drops when pulling the choke out, vs normal fourwheelers which the idle is supposed to raise) but with the choke IN now, it idles low and fine.

NOW: When you give it any throttle, it bogs out completely and backfires or dies.

You can give it 5-10% throttle and get the RPMs up very slowly but if you give it more than 10% throttle it bogs out and backfires/dies.

Have tried adjusting the enrichment screw on the bottom of the carb from 1.0 turn, 1.5 turns, 2.0 turns, 2.5 turns then even 3.5 to see if it helped, but it doesnt seem to make any difference in how it idles at all or how it bogs when under throttle..even when adjusting it a full turn or two while the quad is sitting there idling, it doesnt kill it or change how it idles or dies out when you give it throttle. (I dont know if it should be making a huge difference in the way it idles/runs when adjusting while idling.)

Any advice is greatly appreciated.

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OK. .Sounds like  you  need to  pull the  carb  and clean  it . .You  likely  have  a plugged  high speed circuit. either the  main  jet  or  passages . The  idle  air  screw  should  be  on the  side of the  carb rather than the  bottom.    It  is definitely too  lean under  load off idle..  I  believe  that  carb  has a  diaphragm that  opens the  main  jet  . Check  it  for holes  too. Changing the setting on the  idle  air screw  should  have  large effects on the  quad running . .in  fact , it turned in too  much it  should stall. That's why  I suspect  the  screw  you were  turning  was  not the  idle  air .


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The screw for the air/fuel (bottom of the pilot screw) is definitely on the bottom of this model, but.. found why it probably wasnt making much of a difference.

UPDATE: Took the carb apart, took every bolt out, float, needle, jets, everything and cleaned it all. Took a little less than 1 hour total time.

Definitely gunk in the pilot jet, which is what the screw turns..and also probably why turning it to open wasnt making much difference before.


(SOLUTION/SOLVED😞 After cleaning the carb completely (easy, since there is a video on YouTube showing step by step) and replacing the old fouled out spark plug with a new one, it fired right up and runs fine.

Note: It's still nowhere near as powerful as our 2004 Bear Tracker but it starts in about a half second now, runs good with great throttle response and power throughout the rpms with no stuttering, in-fact better than it ever has..and maybe its unfair to compare it to our other Bear Tracker since this one is a 2000 and the other is a 2004, and is much more powerful. Both run great now.


- Mixture screw is turned out 1 + 3/4 turn

- Carb Needle has the clip set on the second notch from the tip.

(Still wouldnt start for a minute, until i remembered that the spark plug was still the one used when the carb had issues..and even after cleaning was still fouled out.. and Just quickly replaced it with a new NGK plug and the quad fired right up within a second and has been completely fine since.)


If you are bogging out and losing power/backfiring: clean the carb fully (youtube video below making it easy), set your pilot screw to factory setting which for a Bear Tracker is 1.5 turns out, ensure your needle clip is in the factory setting which for a Bear Tracker is first notch or second notch, be 100% sure you aren't getting air through a leak near the carb by spraying carb cleaner around the outside of the carb and rubber to see if the idle changes(a new carb intake boot is less than $15 on Amazon), AND replace the spark plug. ALSO if it does it when you go through water, try unplugging the little electrical plug next to the left hand brake lever since some have a parking brake safety switch which will cause the backfire/no rev issue if the plug, connector or wiring gets wet below..better just to try it unplugged at the handlebars. Also, the airbox HAS TO BE CLOSED TO TEST IF IT RUNS WELL. If the airbox is open when you start it and try to rev it, it WILL bog, backfire and not act the way its supposed to. Some quads will(like our Yamaha Warrior), but the Bear Tracker NEEDS the recirculated valvecover air AND to be closed in a sealed airbox. Last, set your idle to be comfortable while the choke is in the "IN" position and adjust the carb from there. 


THANK YOU GUYS FOR YOUR HELP HERE! I tried to document everything well so the next person with this problem will hopefully find it here and work their way through this forum to their own solution too.


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  • 3 weeks later...

Man this is a great thread. Thanks!  I am having the same issue ( except it doesn't idle with choke off, idles up 1/2 choke, and revs high full). I haven't had time to mess with it but I'm about to go home and check it out again.  The orignal owner stripped out the pilot jet in the factory carb so it can't be removed, but it had a "zoom" carb and both carbs acted the same way.    However I haven't put a fresh plug in it. 

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From my experience... Try adjusting the idle screw/spring on the outside of the carb with your fingers first and set the idle to where (while fully warm) it idles on its own with the choke on the proper "in" position. Even if it runs like junk or doesn't want to throttle or whatever, that is the beginning...since no positive or negative effect you make to the carb will matter until the idle/choke are set properly at warm idle.

A short update...

Since My Original Post: We have only taken our quad for a few brief 1-2 hour or less rides and it has treated us fine.. however compared to our 2004 Bear Tracker it still seems to struggle to find much power in mid-range to top-end rpm compared to our 2004 (seemingly) identical bear tracker which could easily run circles around it. Also, in about an hour of riding we heard one exhaust backfire though it didnt affect how it was riding..so though it runs and drives fine, starts and idles quickly and has driven a couple 1-ish hour rides without any major failure.. I still believe there is something else I could change with the air/fuel preventing it from being 100%. It definitely is rideable and getting very close, but not quite there yet in my opinion.


We have a longer ride coming soon and I will certainly update this forum with the result, since nothing posted here means anything without a definite result once it's 100% and the path of trial and error along the way.

Good luck!

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P.S. If anyone has any good clear method for how to check how rich/lean its running(and how long after turning the mixture screw to check the plug color, if the plug color is the method to be used for checking air/fuel mixture) that would be great.


Also, how long after turning the screw until it should affect the quad's power in a positive way or eliminate backfiring from wrong mixture.



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  • 1 month later...

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