Jump to content

Fcr 39 valve seat question


Recommended Posts

I have been having massive problems with gas in my oil for the last month.  I finally decided to stop being lazy and get to the bottom of it.  From reading various posts on this forum I concluded that the problem was most likely the valve seat o-ring or the float valve itself.  Pulled the carb, and took out the float valve and seat.  The float valve looks fine.  The valve seat doesn't look so good.

1q9iRFxl.jpg?1

Do I need to replace the whole seat or will just the o-ring be good enough?  Is it best practice to just replace the whole thing?  

 

This leads me to question #2.  When I go to this page on jetsrus.com I see that they have 5 different valve seats.  How do I know which one I need.  I have a fcr mx off of a Yamaha wr 426.  

Link to comment
Share on other sites

That is an excellent question.  All I know is that in every forum post about gas in oil the culprit is a combo of the petcock and the float valve.  Honestly, I don't understand why this would lead to gas in my oil.  But ultimately I have no other explanation for the problem and this is a cheap fix.  

Link to comment
Share on other sites

Does the carb you have, not have a hight fuel level drain? I'm wondering why a leaky float valve would put fuel in the oil rather than just pee on the ground?

The high fuel level drain works under most conditions (positions of the bike)

But get the right angles sideways and forward and fuel will still get into the air boot or manifold.

Of course it may be blocked in the brass tube or the plastic drain hose, float level set way to high or a combo of things

Link to comment
Share on other sites

The reason for my question is most (but not all) 36 BSR Mikuni have no high fuel level drain so leaky shutoff valves and leaky carb float valves allow fuel to enter the cylinder and ultimately into the oil.  Where as most (but not all) carbs designed for off road use, including 39 Keihin FCR, do have a hight fuel level drain allowing fuel to drain on the ground when it gets to the top of the stand tube in the float bowl.  So I ask if the FCR you have does have a stand tube in the float bowl for a drain.  Good point about the drain (if there is one) is open.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

×
×
  • Create New...