Question about 2004 Yamaha YZ 125

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2000 yz125 keeps on fouling out plugs

2000 yz125 keeps on fouling out plugs just had carb reworked.runs good for about 5 min or so then you have to putin a pulg.

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  • Murtaza Akberali  Versi
    Murtaza Akberali Versi May 11, 2010

    Its running very rich!. Did you reset the air-mixture screw? Is your air filter ok?

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Fouled plugs are typically caused by jetting that is too rich. This could also be from a dirty air filter which can make the bike run rich. Clean up your filter and see if that is it. If the filter is not too bad, you might want to drop a size on your pilot or main.

Another possibility is poor compression - this can make a 2-stroke run richer than normal as the fuel can not be burned properly. Rings don't last long in these 125s. I used to re-ring each week when I was racing 125s.

You might want to run a B8ES plug, too - this is one step hotter and will help the plug from fouling as often.

Posted on Feb 01, 2010

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Open that **** up u cant putts around on a two stroke or if ur not i might have a fresh top end in it

Posted on Dec 12, 2011

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Hi, Anonymous and the usual suspects are:
1. Fuel mixture too rich or enrichner left out too long.
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Sounds like it could be as simple as a fouled plug. Change the spark plug and try it again. Lugging a 125 around fouls plugs really easily, you have to open it up and clean it out occasionally.

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It's likely just jetted too rich. If you pull your spark plug, it will likely be black and oily. To correct this, you need to alter your jetting. Jetting is not an art - it's fairly straightforward - you just have to physically change the jets inside the carb.

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running the right fuel mixture for the unit if not it could have to much oil & fouling out the plug or not enough oil & getting to hot & melting the piston ring & piston the only other thing is the carb adustments

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1 Answer

My yamaha yz 125 is dumping to much fuel and fouling out the plugs but i need to knoew how to adjust my carb its a 1997


There are only two adjustments to make on your carburetor; the idle speed, and the idle mixture adjustment. If the spark plug fouls frequently, first make sure you are using the correct spark plug. Your 1997 YZ125 uses an NGKB9EGV. Then be sure you are using the recommended two stroke oil, mixed to the proper ratio, in the fuel. Also make sure the air filter is not excessively soiled.
With all of the above confirmed and corrected, start the bike and run until the engine is up to normal temperature. Adjust the idle mixture screw to attain the fastest idle and best throttle response. Then adjust the idle speed.
If you are still fouling the spark plug, verify that the carburetor has the correct size jets by consulting your owner's manual. Keep in mind that if you are operating your bike at an altitude higher than about 6,000 feet above sea level, the stock jetting may be too rich. Down-size the main jet in small increments until satisfactory operation and the correct spark plug color is obtained.

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YZ125 won't start


yeah something you wanna check next, compression. if you can get your hands on a compression tester.

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