The Yamaha OEM factory Service Manuals frequently come up for sale. I've bought 2 on that auction site, but I would suggest that you post here and other places as well. I paid under $10.00 for mine.
I would suggest that you try to find the correct Yamaha manual for your '03 YZ. That way you will have the exact stock settings for both the carb. & the suspension. They really are pretty good.
I've had to lean my '03 125's pilot circuit quite a bit. This helped the low-end response out significantly. You'll want to install the power valve governor spring from an '04 also. I also bought an '04 exhaust pipe for about $30.00