'98 YZ400F Jetting question

1 reply to this topic
  • dbrenize

Posted May 04, 2012 - 05:06 AM


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.

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  • grayracer513

Posted May 04, 2012 - 07:20 AM


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:



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



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