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Fouling plugs

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I have a 04 cr125 and I went out on a trail ride this past weekend and the bike fouled 2 plugs, when I would pull them out they would be covered in a black oily residue, I'm wondering if it was just me not opening the bike up enough because it was my first weekend riding it or if something else could be wrong. this is the year with electric power valves if that makes any difference. I don't think it's jetting because the bike ran great except right before the plug went. Any insight is appreciated! Thanks!

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I have a 04 cr125 and I went out on a trail ride this past weekend and the bike fouled 2 plugs, when I would pull them out they would be covered in a black oily residue, I'm wondering if it was just me not opening the bike up enough because it was my first weekend riding it or if something else could be wrong. this is the year with electric power valves if that makes any difference. I don't think it's jetting because the bike ran great except right before the plug went. Any insight is appreciated! Thanks!

 

Its your carb, the bike is running rich at some point in the throttle, probably towards the bottom end. You can start with the air screw by backing it out, this may or may not solve the issue. If your already 2-3 turns out from all the way in on your air screw you need to do something else. You could probably move the needle clip up, leaning out the midrange of the throttle as a quick fix. Or you can change the pilot jet to something leaner that gives you the best throttle response, and you shouldn't have any issues.

 

Not running the bike hard enough can foul plugs, but this should require lots and lots of idling, the idle circuit tends to be rich, but you should never foul a plug unless you really want your bike tuned that way.

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Its your carb, the bike is running rich at some point in the throttle, probably towards the bottom end. You can start with the air screw by backing it out, this may or may not solve the issue. If your already 2-3 turns out from all the way in on your air screw you need to do something else. You could probably move the needle clip up, leaning out the midrange of the throttle as a quick fix. Or you can change the pilot jet to something leaner that gives you the best throttle response, and you shouldn't have any issues.

Not running the bike hard enough can foul plugs, but this should require lots and lots of idling, the idle circuit tends to be rich, but you should never foul a plug unless you really want your bike tuned that way.

thanks for the quick reply! A friend of mine suggested to mess around with the air screw, but I hair got the bike and I don't know where the screw is on it, any ideas?

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thanks for the quick reply! A friend of mine suggested to mess around with the air screw, but I hair got the bike and I don't know where the screw is on it, any ideas?

I can't help with this because I don't ride a cr but invest in a repair manual, has anything and everything you could need to know about working on the bike. That's the first thing I've always done after buying a new bike or quad.

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thanks for the quick reply! A friend of mine suggested to mess around with the air screw, but I hair got the bike and I don't know where the screw is on it, any ideas?

 

See the red and blue screw? That is your air screw. Turning it in closes off the passageway for air to get into the idle circuit. Turning it out opens up the passageway for air into the idle circuit. Therefore, turning it in allows less air (more fuel) causing a rich adjustment, and turning it out allows more air (less fuel in ratio speak) causing a lean adjustment.

 

And for educational purposes, the large silver screw in the middle is the idle screw. This affects your bikes idle speed by gradually holding the slide open. By the way, these are both aftermarket screws, your screws will just be plain gold ones.

 

Edit: And in response to nholdens post, he's right, get a manual, but don't make the same mistake I did with my cr125 and get an owners manual, make sure you get a service manual.

 

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Edited by dan2581

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Check your trans oil and make sure you are not burning any. That will foul a plug quick. Your exhaust will smell funny and you will have excessive smoke as we'll. usually it is the right hand side crank seal leaking if you are burning tranny oil.

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Ok, I just checked and the bike so leaking oil from what looks like the shifter seal, would that have anything to do with this problem? Also the oil turned to a grayish black color and my local shop said it was a water pump seal so in replacing that also, if that would affect it

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Grayish black is normal, but should be changed. The clutch plates will cause a grayish color to the oil. If it was a milky color, that would indicate water/coolant leaking.

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Grayish black is normal, but should be changed. The clutch plates will cause a grayish color to the oil. If it was a milky color, that would indicate water/coolant leaking.

it did look kind of milky, and I changed oil twice and after every time it would almost immediately go back to the blackish color. I'm using gear saver and it's red so I didn't think it turning blackish that quick was good.

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