black carbon coming out of muffler

5 replies to this topic
  • XR250_RIDER_14

Posted August 24, 2005 - 06:56 PM


Is black carbon coming out of my muffler a bad thing? I just got the 280 kit from xrs only and a hotcam. Just finished my first 20 miles. Should I change the oil and filter now? I have noticed that whenever I rev my engine past 6000 rpms in nuetral black carbon spits out. I stuck my hand in front of it and when I looked at my hand it had carbon all over it. It feels like steam. I am currently running gn4 10w40 without moly. I am burning 93 octane gas. I was curious today and took my spark plug out to look at it concerned that maybe my jetting is to rich??? When I took it out it did have black carbon all over it!! Does that mean jetting is too rich??? It has the same jetting it had before the big bore. The jets came with the xrs only pipe I got from them. They said that the jetting should work just fine. ANY HELP IS APPRECIATED!!!!!

  • AussieXR250R

Posted August 25, 2005 - 12:17 AM


Could be a little rich, in that the larger bore draws more fuel through the jets.

  • XR Pilot

Posted August 25, 2005 - 03:45 AM


Find out what jets people here are using for the 280 kit and compare with yours. Are you definately sure it's carbon not oil? If it is carbon it would seem to indicate your running rich as AussieXR indicated.

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  • mrscullini

Posted August 25, 2005 - 06:16 AM


a little bit of carbon is natural, gasoline is a hydrocarbon.

one of the products of complete combustion is water, so if the exhaust is a little damp, that is okay. this is typically why you see wate dripping from the tailpipes of autos and why the exhaust steams on a cool morning.

does the exhaust smell like unburned gas? is the plug black? sounds like it might be a little rich. list all your mods, the current jet size and your typical riding elevation.

  • johnt3

Posted August 25, 2005 - 04:22 PM


when I went from 250 to 280 and then again to 300, each time I had to lean out the carb. with the bigger bore you will need to rejet leaner each time.

  • XR250_RIDER_14

Posted August 27, 2005 - 08:55 PM


I took out my plug and it was black. The plug seems to have soot on it. I cleaned it with WD-40 and blew it out with the air compressor put it back and and it started with 1 kick. Usually I kick it bout 5 times. It seems like the exhaust is very damp. Its like black steam. I dont know what jets it is. Ill call XRs only and ask them what jets they send with their tailpipes because thats the jets that I have in it. It seems to burn the gas down about twice as fast as it did before. It is ridiculous. I used what I thought was a full tank in 20 miles!!! Please everyone keep watching this thread so I can tell you what jets I have. One more thing is how do I list my mods under my posts like johnt3????

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