jetting, timing, what works best?

1 reply to this topic
  • xrracer36

Posted August 26, 2002 - 01:30 PM


i am just now finding out about the "yz jetting" for wr's... is this a new development?
i knew about yz timing and was afraid to try it, but after racing bro's yz400f while mine was getting top end job, i need more.
is yz timing the ticket, or jetting, or both.
i track ride (mx race) the bike exclusively right now, with a tiny bit of trails.
if i go to yz timing, do i need to rejet?
and what is invovled in yz timing.
i want to know risks, changes and anything else associated with both changes before i make a move.
also, i am aquiring a power bomb header soon very cheaply. will that require a re-jet? i am running a stock yzf muffler.

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  • Hick

Posted August 26, 2002 - 01:47 PM


The "YZ needle" trick is as old as this website, and is not related to the YZ timing.

How 'bout a simple quiz:

Which will affect the breathing characteristics, and therefore jetting, of your WR more?

a) removing the exhaust insert ("uncorking"), thereby decreasing backpressure about 400%, and unsealing airbox ("uncovering"), decreasing intake restrictions by about 100%

:) retarding the exhaust cam timing.

Why is the WR delivered with a different needle than the YZ?

a) Because it has a pinkie-sized exhaust and a sealed airbox.

:D The exhaust cam timing is slightly different.

c) It has lights.

Sorry for the sarcasm, I just wonder how so many folks miss the relevance of the breathing and exhaust restrictions, and their removal, to that weird stock WR jetting.


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