'98 YZ400F Jetting question


1 reply to this topic
  • dbrenize

Posted May 04, 2012 - 05:06 AM

#1

alright this is my first post, and i just got a 1998 yz400f last weekend. has a fmf powercore with a old school fmf header (not powerbomb) and the main is 170 starter is 65 and the pilot is 48. why would any one do this? its like 70-90% humidity here and like 80-90 degrees. like 400ft above sea level. it doesnt staert unless its pop st6arted and runs rich and doesnt idle for long. could this be the starter and pilot being to rich? or just the pilot. does the pilot contribute to starting like the 2 strokes or is it all up to the starter jet? please let me know asap. tjhanks guys.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted May 04, 2012 - 07:20 AM

#2

If you look at the original stock jetting in the first post of the YZ400 jetting DB thread, you'll find that the starter jet is stock, the main is two sizes down, and the pilot one step up. Probably not far enough off to really cause your problem.

The idle circuit, and the older FCR carbs in general, are the biggest reason the 400's are hard to start. First be sure you're using the right method:

http://www.yamaha-mo...troke_vid_a.mpg

http://www.yamaha-mo...troke_vid_b.mpg

Once it's running, check the pilot adjustment using this info:

http://www.thumperfa.../jetting.htm#PJ

http://www.thumperta...ad.php?t=327405





Related Content

Forums
Photo

Should I buy this bike? help....... by Numsa Hul


Dirt Bike   General Dirt Bike Forums   What bike should I buy?
  • * * * * *
  • 10 replies
Forums
Photo

05 yz450f not fast enough by RedeyeYZ


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  38 replies
Forums
Photo

BIGBORE FOR YZ450F 2006? by Taattie94


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 3 replies
Forums
Photo

Snake pit oct 30th by The Anvil


Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies
Forums
Photo

YZ450FX OR YZ450F by MESSMAKER


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

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.