1999 Yz 400 ??

5 replies to this topic
  • JonBrewer1981

Posted March 04, 2009 - 05:48 AM


I just got my first four stroke, it's a 1999 YZ 400, It runs good but backfires and the header pipe glows red sometimes and the bike doesn’t want to idle , I was just wondering if this is normal? It has an fmf power bomb header with the fmf power core 4 muffler. When you’re riding the bike it seems to run good, just backfires and doesn’t want to idle and the header pipe was glowing red. Any info you can give me would be great, Thanks.

  • grayracer513

Posted March 04, 2009 - 07:26 AM


If you let the engine run at a standstill for more than about one minute, the header will glow. Normal.

If you let it run about 30 seconds longer than that (maybe more), it will push coolant out of the radiators. Also normal.

Raise the idle speed a little and adjust the mixture:


Download a manual:


  • JonBrewer1981

Posted March 04, 2009 - 07:53 AM


Ok, That's good to know. Thaks for the info.

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  • 400f mech

Posted March 05, 2009 - 07:29 PM


backfire is a sign of running lean, try getting 1 size bigger main jet or move your needle up one

  • grayracer513

Posted March 05, 2009 - 07:58 PM


try getting 1 size bigger main jet or move your needle up one

Neither of these has anything to do with decel backfire.

  • Birdy426

Posted March 05, 2009 - 09:43 PM


backfire is a sign of running lean, try getting 1 size bigger main jet or move your needle up one

It can also be a sign of running rich...but check the easy stuff first...is the gasket at the header to midpipe joint in good shape and is the clamp tight?

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