YZ timing and GYT-R Insert on WR 400

I have a 2000 WR 400 that has the gray wire and open airbox mods, the jetting is stock. It also has a stock pipe with the GYT-R insert. I recently modded the exhaust timimng to YZ. It pulls really hard in the midrange, but is a little blubbery on the bottom. Adjusting the fuel screw in or out seems to have no effect, it does not even affect the RPM when the throttle is held, and the screw turned.

The RPMs on the top end continue to climb, but the bike stops pulling. The question I have is whether it is the jetting that is off, or is the GYT-R insert that is plugging up the exhaust now that I am on YZ spec?


When I changed to YZ timing on my '99, the carburation became way too rich. I had to go down from a 42 pilot to a 35 and from a 168 main to a 160. I also went to a leaner needle but I don't remember what the size was. Long story short, you need to rejet.

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