Not sure what else i can do to get some more power out of the YFZ. Current mods are -
hmf slip on muffler,
air box removed with intake runner installed,
hot cams intake cam,
exhaust cam retarded,
98mm cylinder with 13/1 compression piston,
flywheel lightened 2 oz.,
Besides porting the head and installing a stroker crank kit im not sure whats left to get some good power gains from.

 

I was reading through your mods, and how hard was it to retard the exhaust cam. also, have you heard anything about cutting the stock exhaust pipe about 4-6" and rewelding it together.

 

after market head pipe probally help, to go with your slip-on

 

Its not too difficult to retard the cam. But i wouldnt recomend trying it if you arent experienced with tearing down an engine.
Why would you want to cut the exhaust pipe? If you mean to shorten the exhaust pipe, that would move the power curve higher in the RPM range assuming you didnt shorten it too much. 4-6" might be too much. But i dont think you would get a huge increase in power from shortening the pipe. Then again i dont know, im no expert. Not sure what youre saying.