2008 YZ450f Exhaust Smoke

23 replies to this topic
  • markitos020

Posted July 17, 2013 - 09:16 AM


Timming chain is not new but i ordered a new one and will replace it when it arrives, filter only has one ride its brand new but I run on heavy mud and tight trails its been raining all month here but i clean it after every 2 rides, about the cilinder i installed a new one along with the new piston, im thinking the same as you, clearance might be tight since i did shim them on the bench not installed.... i will be cheking it today after work and posting the results, problem is i cant be sure if the problem is fixed until I ride on the trails since the problem only occurs when the bike is really hot.

  • markitos020

Posted July 17, 2013 - 02:44 PM


I checked valve clearance and they are out os spec. Intake valve timming chain side is .006 inch middle is .004 in and clutch side is .007, both exhaust are at .008 whats the best number to set them at? I must clarify that the valves where within spec before but i installed bigger shims on intake since they were all on the high side of specs and wanted to bring them closer to the middle of specs but i guess bench clearance is not the same when installed. What clearance should i set them to i do have specs but is it better to be on the high or low side? Thanks

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  • NitrousR1

Posted July 17, 2013 - 02:45 PM


I'd start with one size bigger pilot jet being you are at 4 1/2 turns out. Test it afterwards and see where it's at. You might have to even go up again possibly. I'd get rid of that fuel screw, get a good name brand one. Not worth wasting your time and everybody else's time here with a once bent fuel screw

  • grayracer513

Posted July 17, 2013 - 03:38 PM


Since the entire range of clearance specified for either valve is only .002" wide, it matters very little where it falls within that range. Technically, tighter is preferable, but it just doesn't make that much difference.

If the bike idled and ran with the jet that's in it, it should again. But, 4 turns out indicates a too small pilot, so what happened? Your pilot jet has probably been downsized by a layer of fuel varnish from sitting around while you fixed the engine. The orifice in the jet is so small that a film no more than .002" thick will take a pilot from a #45 to a #35, more than 20% smaller, and way out of range.

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