Fouling Plugs

Joined
Apr 24, 2007
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#1
Ok well i have had my yz125 for about two weeks now and i love it! But my main problem is fouling plugs i have fouled 2 or 3 in these past two weeks. From what i have noticed today after fouling the plug yesterday is that when i am going around the corners is my main problem. I ride in a lot on a lot of big farms and it runs great when i am there, but at my house all i have are trails i have made in the woods and they are tight. So when i turn i have to slow down a lot, and i have noticed that it bogs then and i have to get back on it hard quick or else the plug will foul. So i am guessing that it is running a little bit to rich? So how should i go about fising this should i adjust the carb or just change my fuel mixture i am running it 32:1.
 
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Oct 19, 2006
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#2
Changing the oil mixture is not the way to fix a foulding problem. I've run bikes between 16:1 and 40:1 in all kind of conditions, with a cold plug, without ever fouling the plug. You probably need to rejet. It sounds like the transition from the slow speed circuit to the mid throttle is getting to rich. I would first try raising the position of the clip on the trottle needle one to two positions. This will lean out the part-mid throttle a little bit. It costs nothing to do and will give you a bit of a baseline as to where to start.
 
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May 27, 2005
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#3
Normally the jetting on the later YZ125's is pretty close. I am taking from your post that its only fouling when riding on tighter trails etc? Is the bike running OK before it fouls? (You mention a bog but am not sure you mean it bogging from being to rich or just not in the power band?)

With a 125 it could be you aren't getting the plug hot enough to self clean itself when trail riding it as you aren't on the trottle as much and are at no throttle more than a track or open trails. I recall the YZ has a BR9EG stock; you may want to try a BR8EG (or BR8ES to save some $$) when trail riding; this can help the plug stay hot enough to clean itself. Then run the stock BR9EG when on more open tracks or trails.

This assumes the jetting is on or close and that the problem isn't from a dirty or over oiled air filter. Once you have ruled these out; then try one step hotter on the plug to see if it helps the fouling.
 
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May 6, 2007
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#4
How do i adjust the clit on the needle. Someone told me to do that to my 06 CR125 but i got the carb apart and dont understand where you adjust it at.
 
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#5
Well if you move that clip up, that will make the needle sit further down, which would cause it to sit further into the main jet hole, which would lean it out at 1/4 throttle. The needle is what is stickin out of the slide in the carb, that the cable is hooked on to. You should get a manual if you dont have one.

You could also try to just remember to open up the throttle every few minutes to clean out some of the unburnt fuel in the exhaust valve.

If i bog my yz125 too many times without letting it into the powerband it will also foul a plug.
 
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Apr 24, 2007
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#7
Yes it has only fouled plugs on me on tight trails, and yes it runs great before hand and when i say bog i mean because of it being to rich or atleast thats what it feels like to me. and to answer 76GMC's question i downshift to either second or sometimes first, and i make sure it keep the rpms up the best i can.
 
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#10
How many people on this thread and who's bikes carb has a clit?Boo it sure sounds like you are lugging the motor and it is falling on its face,in a safe area,get it to bog and fan the clutch,I highly believe you will crash!To much throttle and to high a gear or to slow of a speed and you are killing the motor!A 125 wants to get up and sing,let that baby RIP!Do not start throwing different plugs at your bike like a dart board,learn to read your plug.A bike loading up,poorly jetted,or a mechanical problem can all attribute to the same sparkplug foul.
 
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Feb 11, 2005
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#11
your just letting it run too slow (rpm's) around those turns. a two stroke wants to be ripped all the time, especially a 125. if i let my rpms drop too much, ill have the same issues. work your clutch a little more around those turns, keep the bike in the power band, and youll have no more fouled plugs.