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fouling spark plugs on a 2001 yz250f

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bike is a 2001 yz250f. it seems every couple rides and some times every ride the plug stuffs up. it has a little bit of corrosion on it and one time it had heaps of corrosion. im sick of it. it seems i have to change it before every ride. i have known the bike my whole life and owned it for the last 3 years. today it had a charcoal black tip and further up it was wet. it had very very little corosion. its only started happening the last few months. which also happens to be the same time my dad started riding it as a bought a new one. the engine is pretty old could worn rings or piston or some thing like that be the cause. im thinking the spark plug cap is old and worn letting moisture in when a wash it causing it to corrode. also my dad is very slow.kind of just toots around. would this have some thing to do with the matt black tip? i dont think its the head gasket causing the corrosion. been happening the last 10 hours or so. is it still safe to go for a few more rides?

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When you say corrosion, I'm assuming it is on the metal exterior of the plug. You are associating two problems with one cause. The corrosion on the outside has nothing to do with the plug fouling.

Corrosion on the outside is from the washing as you describe, but it may not be the fault of the cap. There is a small drain hole at the bottom of the sparkplug well (right where the threads start) that's probably plugged with dirt and not letting water drain out. On the right side of the cylinder head just above the head gasket, you will see where this small exits.

The fouling is from the jetting being too rich, or as you mentioned, the engine is due for a top-end.

sparkplug.jpg

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the bike is not burning oil. the weep hole was not blocked. so its got to be something in the carb. to rich or to lean? i think some thing is blocked. what do you think

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Carbon fouling is cause by too much fuel. Dirty air filter, leaking needle/seat, bad float or level set incorrectly, or carb jetting too rich.

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yeah but nothing has changed. why did it start fouling now? the air filter is all ways clean. can the float level change by its self? to much fuel or maybe not enough air? what would you recomend to make it leaner? i would think its oil weeping from the piston rings because its done alot of hours but it's not burning oil and has good compression

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Parts wear out and dirt gets places it's not wanted. You could have some debris in the needle/seat ot the needle may need to be replaced. Plastic floats also deteriorate over time depending on what type of fuel they are exposed to.

The needle in the slide will wear out too. It's constantly rubbing on the needle jet as the throttle moves and it doesn't take much wear to upset the jetting.

If you have a worn out cylinder, piston, or rings, there will be visible bluish/white smoke when it's running.

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I have a brand new 2010 yz250f that fouled a plug after about 1.5 hours. I have about 3 on it now. We'll see if it continues to foul them. I've got a DR650 with around 13,000 miles and never fouled a plug. Not real impressed with the new yz250. Both bikes run great and seem to be jetted correctly. Who knows.

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yeah my 2010 yz250f has never fouled a plug at 50 hrs. but my 01 has fouled about six in the last 10 hours. its never fouled while riding only when i go to start it up again.

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there is no smoke out the back. so it must be carb related? maybe electrical

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Electrical problems don't cause plug fouling. One problem I have encountered in the past is variation in fuel quality and old or stale fuel causing fouling.

If the fuel in the bike is more than a few weeks old, get rid of it (burn it in your pickup), and get some fresh fuel from the gas station. Fuel stored in anything other than a sealed (airtight) metal container will not last forever and can cause major headaches when it is stale.

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bike gets ridden every week. but only for about 30-40 mins. just re-jetted it. its running way better. went from 175 main to 170. needle is in the same posi but thinking of taking it up one

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bike gets ridden every week. but only for about 30-40 mins. just re-jetted it. its running way better. went from 175 main to 170. needle is in the same posi but thinking of taking it up one

If you pull the needle, look at it very closely. If you see any shiny spots or any indication of wear, no matter how small, the needle should be replaced.

A worn needle will definately cause a rich mixture and plug fouling.

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The needle has a light gold colored anodizing on the surface when thet are new. It hardens the surface to prevent the soft aluminum from wearing. When the anodizing is worn though the color will change to silver and shiny.

If you see any wear spots on the needle (except for the top 1 inch) it should be replaced. Like I said before, it doesn't take much wear (only .0001 inch) to upset jetting.

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