Black deposits around the tail-end of the Exhaust

12 replies to this topic
  • akanana

Posted December 06, 2008 - 07:34 AM


I am experiencing black deposits around the tail-end of the Exhaust of my 2007 YZ450F. Also, the bike is some-what easer to kick now. I have about 50 hours of mostly easy riding (no racing). The bike consumes a little bet of oil of about 100-110ml for every 3 hours of riding. My question is: I am due for piston/rings/cam chain replacement? Or can I get say another 20-30 hours of riding without damaging the engine. Thanks in advance for your replies.


  • finthat

Posted December 06, 2008 - 08:26 AM


I'm no expert but it sounds like topend. If it is easier to kick probably rings ect.

  • Deathdeelr

Posted December 06, 2008 - 10:14 PM


I would second the motion for rings but could your mixture be off. Oily deposits definitely say rings but a dry black deposit could mean too fat a mixture.

  • JSanfilippo

Posted December 06, 2008 - 11:16 PM


I would second the motion for rings but could your mixture be off. Oily deposits definitely say rings but a dry black deposit could mean too fat a mixture.

I second this.

If its dry the bike is probably just running a little fat. Have someone ride behind you and tell them to pay careful attention to what comes out of the exhaust when you're hard on the gas. If its black and sooty, its just a rich air/fuel mix. If its the blue stuff that usually comes out of clapped out CRFs then yeah your rings are shot.

  • magiksc

Posted December 07, 2008 - 09:58 AM


How much easier is it to kick? It will obviously become a little easier after breakin and some time but if it is like night and day with only 50hrs then I'd agree with the rings.

  • BC3

Posted December 07, 2008 - 08:32 PM


[COLOR="Blue"]Typically unleaded fuel (Pump gas) doesn't color a spark plug...And will leave a black deposit on the exhaust pipe (Muffler tip) If the bike runs good,Idles, and starts easy....Just ride that thing and stop worrying about the black on the pipe...they all have it with pump gas...Regular service, valve adj. oil and filter change,
tighten all the fasteners.... [/COLOR]

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  • Deathdeelr

Posted December 07, 2008 - 08:56 PM


Use, abuse, throw away, and buy new! (or at least tear it down for a refurb):thumbsup:

  • davegod

Posted December 08, 2008 - 08:56 PM


the bike mags get 150 hours out of a 450 with little wear to show for it.if you service your bike by changing the oil frequently and cleaning your air filter every 2-3 hours depending on conditions you'll get plenty of life out of that bike.i change the oil in my wr450 every 110-120 miles.i chang the oil filter every other time and use only factory spark plug every 500 miles.these yamahas are very durable.don't run it with the oil low and check your coolant before every ride. check your jetting though,sound a bit you have an aftermarket air needle?:thumbsup:

  • cbreakin

Posted December 10, 2008 - 08:14 PM


With the auto decompression systems on these bikes is it possible to judge the compression of the motor by kicking it over. It seems that it should be "easy" as long as the auto decomp is working:excuseme:.

  • grayracer513

Posted December 10, 2008 - 08:23 PM


Auto decompression is a compression reducer, not a compression release. It works by shortening the compression stroke by about 40%, so that the engine has more like 7:1 compression than 12. Compression tests are meaningless, but leak down tests are valid. Even though the bike will be easier to turn over than one without AD, it will still have some compression resistance, and as they get tired, that resistance will get even lower. You can tell the difference in the kick crank.

  • akanana

Posted December 11, 2008 - 02:36 PM


Thanks to all for their replies. Yes the bike has been meticulously maintained since I bought it new. Synthetic oil every seven hours, oil filters every second oil change and cleaned air filter every second ride. Overall the bike runs and starts fine with no issues. I have not had a chance to ride since I posed the question, but a rider had told me that he smelled gas coming out of my bike as he was riding behind me. So maybe it is running rich which cased the black deposits. I will check if there is any blue smoke coming out which will indicate top-end job is needed. Thanks again and will keep you posted.


  • Ga450owner

Posted December 12, 2008 - 07:38 AM


I believe you just answered your original guess is that it is running rich and needs to be rejetted.
If it is smoking you got topend and/or valve sealing problems

  • minton227

Posted December 12, 2008 - 07:47 AM


Sounds to me like the bike is running rich, like you said. That would explain the gas smell cause nat all the gas is burning due to lack of air in the mix. Check your spark plug to make sure. It should be golden tan. If it's black, then you are running rich.

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