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Everything Dirt Bike
Make / Model Specific
Yamaha
99’ YZ400f ABRUPT BLUE SMOKE
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<blockquote data-quote="SRAD97750" data-source="post: 232561" data-attributes="member: 425"><p>Probably Piston Rings or Valve Seals.</p><p>I suspect rings based on your description. Excessive ring end gap.</p><p>With worn piston rings, exhaust will be fine on initial starting, but then pour smoke and reving it makes it worse.</p><p></p><p>With bad valve seals, smoke is strong initially and usually clears up after a little bit and smokes more gently. Parking it for long period makes the smoke worse as it's had time to puddle on the back of the valves.</p><p></p><p>-BIG DAN<img src="https://www.dirtbikeaddicts.com/static/images/smilies/thumb.gif" class="smilie" loading="lazy" alt=":thumb:" title="Thumb :thumb:" data-shortname=":thumb:" /></p></blockquote><p></p>
[QUOTE="SRAD97750, post: 232561, member: 425"] Probably Piston Rings or Valve Seals. I suspect rings based on your description. Excessive ring end gap. With worn piston rings, exhaust will be fine on initial starting, but then pour smoke and reving it makes it worse. With bad valve seals, smoke is strong initially and usually clears up after a little bit and smokes more gently. Parking it for long period makes the smoke worse as it's had time to puddle on the back of the valves. -BIG DAN:thumb: [/QUOTE]
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Everything Dirt Bike
Make / Model Specific
Yamaha
99’ YZ400f ABRUPT BLUE SMOKE
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