YZ 400 carb leak??

7 replies to this topic
  • Michael Cahill

Posted January 02, 2008 - 12:55 PM


I just recently pulled out my carb because i noticed there was a small fuel leak comming from the over-flow line, even when the bike was just sitting there. :busted:

so i pulled out the carb, checked the float and flot seat. and they are bolth fine, and set to spec. (from the manual)

so obviously somthing is wrong with the float system, but what??

do i need to replace the valve, or simply just need to readjust it a different way?? :banghead:

Thanks, Michael

  • grayracer513

Posted January 02, 2008 - 01:42 PM


Be sure you adjust it correctly, by holding the carb at an angle, per the manual. If you can't do that, you have to be careful to apply just the correct pressure to the float when measuring.

Two things can cause the needle valve not to seal:

> Dried out, shrunken, cracked, or worn needle valves, or

> Dirt. Any dirt. The tiniest little invisible speck of dirt. Be sure it's clean

The only cure for the first problem is to replace it.

  • Michael Cahill

Posted January 02, 2008 - 02:10 PM


I see

now ive never had any problems with it before, it just started leaking one day after i was ridding. ( i know that sounds like dirt, but i checked and cleaned it when i pulled it out,) but its still leaking.

now when i check the float, what angle should i hold it at?
it dident make sense the way the manual put it.

  • grayracer513

Posted January 02, 2008 - 02:21 PM


Look at the second picture on 4-11 in the manual. Hold the carb with the float hinge pin horizontal, and the float hanging down and free (not touching the needle against the seat. Rotate the carb more toward upside down, so that the float begins to swing toward the carb body. As soon as the float arm contacts the needle valve, or the needle valve contacts the seat, stop and measure the level.

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  • Michael Cahill

Posted January 02, 2008 - 06:26 PM


oh ok i see,

ill let ya know how it goes.

now if the valve is worn out, is there a way to tell by looking at it?
because from last time, it looked fine, no grooves or anything.

  • grayracer513

Posted January 02, 2008 - 07:59 PM


If a valve wears, it will loose clearance. If it hasn't lost any clearance, it hasn't worn.

  • bustersat

Posted January 03, 2008 - 04:07 PM


I had the same problem with my 02 426. Replace the needle valve set and you should be fine. Even though it looks ok , there can be shrinkage (I was in the pool!), hardening or cracks that cause this.

  • Michael Cahill

Posted January 03, 2008 - 08:06 PM


oh ok,

well i took her out and rode around for a couple munites, to see if that would clear out any small dirt particles, and apperently it worked! :banghead:

now its not leaking anymore, so im just going to keep an eye on it, and if it keeps leaking i'll just get a new valve.

Thanks guys :busted:

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