timing/jetting question

I have a 2000 wr400 which is wr timed and has an fmf powercore 4 S A. I am very happy with the jetting. If I yz time it will I have to monkey around with the jetting again?



I did the YZ timing before I added the FMF power core IV and power bomb header. without changing the jetting the timing moved the power up in the curve. When I added the pipe I ended up with a hesitation at 0~1/8 throttle. I have turned my pilot jet air screw out to 2 3/4 turns out and dropped the clip to #4 possition and eliminated 90% of the problem. Now I have a needle on order and the BK mod to hopefully take care of the last 10%.

I was very disappointed with the change to YZ timing until I started making the other changes. Since you already have the pipe in place, I would say it would be easy and cheap to make the change.

Just my 2 cents.

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