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Oil fouled plug Yz 125

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Hello everyone I am working on a 2000 Yz 125. When I first got the bike it wouldn't crank at all. So I found out it was the stator, I replaced it and the bike fired up instantly.

After letting the bike warm up, I start off riding and I shift through all gears until almost top speed and the bike dies instantly. Once the bike shuts off it will kick and fire right back up instantly. Another ride top speed again and the bike shuts completely down.

After one day of riding now the bike will not start. I removed the plug and it's very black and oily it looks. I removed the cylinder head and piston is pointing in the right direction. I also checked the reeds, they are perfect. The plug need replaced but what steps do I take next is it the carb, power valve , main seal, low spark etc ?? Help anyone

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Dude, why are you messing with all the hard stuff?  Just replace the plug!!!  Always start with the simple stuff.  It's a two stroke and any problems are likely to be very simple.

 

The stock heat range on a YZ 125 is a "9".  Go to any autoparts store and by a few BR9ES plugs, and a few BR8ES plugs.  They cost like $2 a piece--at most $2.50.

 

Mix up some fresh 32:1 and make sure the air filter is clean.  Try the bike with a 9.  If it works fine, your good to go.  It if works for a while but then fouls, you have to options:

1. The easiest thing to do is just try the 8.  They may solve your problem.

2. The more involved method would be to alter the jetting with the 9 (start with the needle clip--probably all you need), and then move to an 8 if you can't get it to run clean with a 9.

 

I have 2 yz 125s myself that I use for woods riding and racing.  One runs best with a 9 plug and mildly altered jetting.  One runs best with jetting nearly stock (1/2 step needle) and an 8 plug.  

 

Finally, just out of curiosity, have you tried that old stator with a new plug installed?

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Raise the clip on the needle in the carb and drop down one jet size pilot.adjust according too with the air screw it in all the way back it out 2.5 turns then in until you get proper idle and crisp throttle response if it still eating plugs drop the Main down one more again. You will just be wasting your money buying plugs do it right that bike will rip.

Edited by YzCas

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If despite a new plug and leaner jetting it still oil fouls plugs like crazy,

 

keep track of the gearbox oil level, making sure it isn't being sucked past a worn crank seal.

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I rode the bike today, i got the bike to top speed once. The other two times I hit all gears then the bike bogged down and wouldn't crank. So changing the jets should work?

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If it got to speed properly at least once, it pretty much rules out any jets being blocked.

 

Your last description sounds more like a fuel delivery problem: float height too low, sticking fuel inlet needle, blocked gas tank vent.

Or, some electrical component that shorts out after a while when it gets hot.

 

Unless the engine is modded a lot, or the ambiant temps are much hotter or cooler than usual in your area,

the stock jetting should be in the ballpark to get it running somewhat decent, pending the engine is in good mechanical condition.

(no air leaks, good compression, good crank seals, good reeds etc.)

 

If the ignition system and fuel delivery are found to be ok,

doing both a compression test and a crankcase leakdown test could rule out many potential problems instead of guessing.

Edited by mlatour

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Raise the clip on the needle in the carb and drop down one jet size pilot.adjust according too with the air screw it in all the way back it out 2.5 turns then in until you get proper idle and crisp throttle response if it still eating plugs drop the Main down one more again. You will just be wasting your money buying plugs do it right that bike will rip.

so i should raise the clip

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