yzf jetting issues


3 replies to this topic
  • rmx250rider

Posted June 21, 2009 - 12:59 PM

#1

it is a 98 yz 400, and I bought it a couple weeks ago the main is a 175... it has a fmf powercore 4 and ready airfilter with backfire screen takin out... 175 is stock and tried a 180 and it bogged bad down low but was awsome up top so I went back to stock... problem now is that it is getting hotter by the day and its getting harder to start.
it always started 1st or 2nd kick... and now it takes more then 10 or more to start, but once it warms up it starts up fine and dont have an issue

should I go down on the main or try something else?

  • ajeb

Posted June 21, 2009 - 01:27 PM

#2

it is a 98 yz 400, and I bought it a couple weeks ago the main is a 175... it has a fmf powercore 4 and ready airfilter with backfire screen takin out... 175 is stock and tried a 180 and it bogged bad down low but was awsome up top so I went back to stock... problem now is that it is getting hotter by the day and its getting harder to start.
it always started 1st or 2nd kick... and now it takes more then 10 or more to start, but once it warms up it starts up fine and dont have an issue

should I go down on the main or try something else?


A main jet only effects the engine performance from about half throttle through to wide open throttle. It had no bearing on your low end
performance.
Always adjust your main jet for best top end performance at wide open throttle.

Your pilot circuit comes into play when starting, at idle and small throttle opening, from closed to about quarter throttle.

Check your pilot jet and fuel screw settings and report back. You may have too richer setting on your pilot circuit for the warm weather.

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  • grayracer513

Posted June 21, 2009 - 09:39 PM

#3

You may have too richer setting on your pilot circuit for the warm weather.

You're correct otherwise, but you have that reversed. Warmer weather requires that you adjust leaner to compensate.

Trim the idle adjustment correctly:

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

  • ajeb

Posted June 21, 2009 - 10:56 PM

#4

You're correct otherwise, but you have that reversed. Warmer weather requires that you adjust leaner to compensate.

Trim the idle adjustment correctly:

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


Thats what i was saying, meaning the pilot circuit is too rich... I think my wording is a bit confusing. :worthy:





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