98 yz400f carb issue...Help


4 replies to this topic
  • Torqd

Posted March 19, 2009 - 02:34 PM

#1

This is my first yamaha and I got it second hand. So I have no idea what the stock or uncorked jetting should be. The FCR carb has three jets in it. I know what the main jet is but the other 2 are kinda wierd. I would call #21 in the diagram below the pilot jet... I am not sure what jet #20 is. My bike was having a hard time running without the choke on and the fuel screw was like 3.75 turns out. Pilot too small. Of course I already cleaned the carb before you start asking :-) The diagram and my local dealer says #20 is the pilot and it should be a 65 but mine had a 45 in it... and it say #18 should be 45 and I have a 50... and the main should be 175 and I have a 180.

I am a little confused. I read many have a 48-50 pilot but stock is 65... doesn't make sense. My dealer only had a 54 so I am not sure what to do.


If anyone can shed a little light on this for me it would be great.


http://www.yamahaoft...r=1998&fveh=861

  • grayracer513

Posted March 19, 2009 - 02:53 PM

#2

To start with, your dealer is wrong; #20 is the starter jet, and is functional only while the choke is open. #21 is the pilot.

Here is the original jetting:
  • Main Jet: 175
  • Pilot Jet: 45
  • Starter Jet: 65
  • Leak Jet (if any): N/A
  • Fuel screw/Setting: 1.5 - 2.5 turns out
  • Needle/Position: OBDVR/4

Here is a link to jetting used by other users:

http://www.thumperta...ad.php?t=694914

You may have a problem with the slide spring plate, item #12 below. It is often installed upside down by mistake, and will sometime crack, or break off a corner, causing poor engine operation at part throttle.

Also check that the hot start valve is closing all the way, and that there is no air leak in the line leading into the intake port.

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  • jayh300

Posted March 19, 2009 - 03:02 PM

#3

i was clicking the yamaha of troy link... the jets are listed backwards in the text...
20 is 21
same on bike bandit on the 98 model went up to the 99 i had and they are correct... silly parts books

  • Torqd

Posted March 20, 2009 - 05:05 AM

#4

Thanks guys... that makes sense... Nothing like factory parts books being wrong and a dealer not knowing whats up. Oh well. I will check the plate and look for leaks. I will go get a 48 and mess with it today. Unemployment has some benefits :-)

  • Calitoy

Posted January 22, 2010 - 08:01 PM

#5

how is #39 in stall it has someting thath it looks like is conected
with the trotel cable





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