1999 YZ 400f Carb issues

6 replies to this topic
  • ryan2214

Posted October 03, 2010 - 07:01 AM


I have a gas dripping (sometimes pouring) from the very bottom over flow line of the carb.....any ideas?????


  • DeeCee

Posted October 05, 2010 - 04:12 AM


Your carburettor is overflowing because the float valve is not shutting off.

This can be caused by dirt under the valve, a worn valve, or incorrect float height.

How long has the problem been happening. If it just started, give the float bowl a tap with the head of a screw driver, sometimes this helps dislodge some dirt under the valve and fixes the problem. If this doesn't work, you will have to strip the carburettor.

Also see other posts of today's date on this subject for a 400F.

  • tattoo79

Posted March 25, 2011 - 09:15 PM


just got this 99 yz400f bike on a trade and the header on it got red hot....wow whats going on there?

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • DeeCee

Posted March 26, 2011 - 07:23 AM


The YZ400 does not like being left at idle for too long, it prefers to be moving. Also the header pipe is very thin so extended period of idle will cause the header to glow. This is a common observation. If you search the forum you will find you are bot the first to have shown concern at a red hot header.

  • tattoo79

Posted March 26, 2011 - 03:47 PM


thanks for the reply...yamaha said i was running way too lean and that it could seize the bike up.....it glows red almost as soon as it warms up...im going to melt my leg off and then light a smoke off the header:banghead:

  • tattoo79

Posted March 26, 2011 - 06:02 PM


ok so i got the bike out in the open and no red glow...runs like a raped ape...and idles fine....one more concern though,,the over flow tube that hangs down at the bottom of the motor drips alittle oil...ok im fine with that its there for a reason, but the oil looks alittle milky...but then again the motor was just rebuilt....do i have a need to be concerned...is it a blown head gaskett?? or should i take it out for a couple rides and see if it clears up?

  • jojo1224

Posted March 26, 2011 - 06:47 PM


It will drip oil, it may also look milky. My old yz426 would coat my boot in milky looking oil with both motors I had (stock and 444).

Related Content


Wilson the Blue Privateer by jetfuel

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  50 replies

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

James Stewart back on a YZ450F by YamaLink

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies

Is it worth it? (Cam and High compression piston) by macgi77

Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  30 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.