If you choose to go with new pipe, the Dasa is probably one if not the best option for pipes on a YFZ. The produce great power for both piped bikes to built bikes.
If you haven't already, I would check the jets again, so much old gunk in those carbs, they might become clogged or check for air leaks. Are you still using the stock air filter also?
Replaced both pilot and main jets? I have to spray the heck out of mine the first time I went to clean it, probably took 3 cleanings, spraying every little hole and crack out!!
I also had air leaks, I pulled the intake manifold off and had to replace the gasket and some have seen splits in the intake boot.
Has anyone tried the General Grabber tires? I saw an all terrain set on a truck yesterday and they look like a nice tires.
http://www.generalti...m/tires/Grabber