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95 YZ125 Fouls Plugs

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My bike keeps fouling out the plug. I have cleaned the plugs, air filter and carburetor. When the problem happened I was out riding and it just starting bogging (my thought was a foul plug). I changed the plug and it would foul again in a minute or so then not run the engine. This is when I cleaned the air filter. After that it would still bog down, but not foul out completely where the engine couldn't run. Cleaned the carb here still the same. It seems to bog around mid throttle.

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Bump, I don't know if these are aloud. I looked for thread rules on the forum, but couldn't find them.

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sounds like a jetting issue more than anything. plugs typically dont just go bad to make you angry. they go bad due to bad jetting or some other goof. ask some of the jetting gurus on here for help and they may be able to help you A LOT more than i can

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If you've been riding when it was cold and when the weather warmed up this problem started, the bike is probably running rich.

If it bogs at mid-throttle and doesn't bog at WOT, drop the needle a clip or two and see if that helps.

If it bogs at WOT, drop down a size on the main jet and see if it's better. Might need to also open the airscrew a tad if the carb was tuned for colder weather and you haven't tweaked it lately. Also, write down what the air temperature and humidity is (if you know it) and what your MJ size is for future reference. Make sure that you stay on the rich side of the lean peak so that you don't burn the piston.

If you're oil-fouling, try a different batch of gas. It's been more than once that I double-dosed a jug and didn't notice it till later. :thumbsup:

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The thing that I don't understand is I was out riding (I ride in my yard) and I went over to my deck and turned off the bike to talk to my dad. Then I went back out and it fouled the plug. I put it away and later cleaned the plug and topped off the motor oil. So it just happened out of nowhere.

@davidl9999, the only time I've used it in the cold was this past December for a friend's college project. It was only one day and the temperature was like in the 40's or 50's (I'm outside of Philly in Pa). After that I have used it once it got warm again.

At full throttle the exhaust pops probably cause it bogs while getting there? And getting new gas is the only thing I didn't do involving the fuel system, I've checked and cleaned everything else from the air filter to the reeds.

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The thing that I don't understand is I was out riding (I ride in my yard) and I went over to my deck and turned off the bike to talk to my dad. Then I went back out and it fouled the plug. I put it away and later cleaned the plug and topped off the motor oil. So it just happened out of nowhere.

How much oil did you add? If you added too much drain it and add 650ml of oil.

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I was adding in small amounts watching the level check bolt, but I can empty it and add 650ml which is 20 some oz.

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Correct use 650- 700ml of motor oil in the tranny, adding too much could cause you to blow a right side case seal. The check bolt from the factory is wrong on just about every single Yz Ive ever worked on or owned.

Also did you replace the plug or just clean it? NEVER reuse a plug after it has been fouled. Most of the damage done by plug fouling is too deep in the spark plug to be cleaned. Try those two things and see if it fixes your problem. Spark plugs are too cheap not to replace them afte they foul.

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I cleaned the spark plug, we have a plug cleaner that hooks up to the compressor.

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Go buy a new one!!! Im willing to bet money that thats where your problem is. These 2 strokes are very finicky with spark plugs! They dont like to run on spark plugs that have been fouled.

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You can heat up the plug to about 300 degrees celsius and clean it that way, better than just letting it dry up. Also how do you ride your bike, on the pipe? When does it fould the plug? Low end / middle or high at wot?

Regard

Arnego2

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@ftball90, I take a trip to Napa, get me some plugs.

@arnego2, I don't ride hard with full throttle, I do hit the powerband once in a while. I ride with utility quads, so I usually stay with them.

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Hello

well without trying to offend you but that could be the very reason why your plugs foul on you. If you hardly ride at the pipe you need a by far leaner jetting IMO. I sold a 125 with 55/NP3/185 jetting ot a kid and the plug was brown. The he came back with fouled plugs and spooge sipping out of the silencer. I believe I went to 45/NP1/170 and it still comes up pretty black. But it stopped fouling plugs.

Regards

Arnego2

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@arnego2, what is at the pipe, sorry if I'm not with the words. Then this is the first time the plugs fouled, I've owned it for at least 5 years.

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I used the stock pipe and have done the silencer packing.

You could have a look at the clutch side to see if the bearing as some movement.

It should not have any if it is correct.

Good luck

Arnego2

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@arnego2, what is at the pipe, sorry if I'm not with the words. Then this is the first time the plugs fouled, I've owned it for at least 5 years.

Riding on the pipe means keeping the RPM's up and the PV open to clean stuff out

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PM me and let me know your riding style, engine, make model etc and I will set you up with a plug that won't foul on you.

MX bikes (especially 2 strokes) have plugs that reach a self cleaning temperature when the bike is placed high in the revs (as said on the pipe). If you are idling long and aren't high in the revs often enough you will foul plugs or cause poor running due to carbon'd / oil'd up plugs that tend to misfire. Using the correct heat index plug for your riding style should solve that problem without the need to re-jet.

If you can post a picture it will tell me a 1000 words.

Hope that helps.

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PM me and let me know your riding style, engine, make model etc and I will set you up with a plug that won't foul on you.

MX bikes (especially 2 strokes) have plugs that reach a self cleaning temperature when the bike is placed high in the revs (as said on the pipe). If you are idling long and aren't high in the revs often enough you will foul plugs or cause poor running due to carbon'd / oil'd up plugs that tend to misfire. Using the correct heat index plug for your riding style should solve that problem without the need to re-jet.

If you can post a picture it will tell me a 1000 words.

Hope that helps.

I have some of it apart right now and when its back I can take a picture of the plug (assuming that's what you want to see).

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I have some of it apart right now and when its back I can take a picture of the plug (assuming that's what you want to see).

Yes, the bottom of the plug that projects into the combustion chamber. The color will tell the tale and let me know how often your on the pipe. I will be able to gauge with that what plug you will need.

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Why not just tell the guy to go 1 heat range hotter at a time until he gets a reasonably non-black insulator, and if it's white, it's too hot?:thumbsup:

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