If it hasn't been done already, get the Honda Power-Up carb manifold, carb needle, and exhaust insert. Then pull the snorkel & restrictor plate out of the airbox, and install a 175 main jet. Aftermarket exhausts are just eye candy, and some can actually rob power. I know a lot of guys were swapping their stock carbs for Edelbrock Qwiksilver pumpers, but I never had trouble with the stocker.
Yep, I've done those. Only I cut my exhaust tip with a hole saw instead of paying the bucks for the Honda unit. Also I'm using the stock carb instead of the sooper-dooper Qwiksilver carb. Seems to work just fine here in Atlanta w/ a 170 main and 1 step hotter plug. I have just cut two triangle shaped holes in the left number plate like the factory desert bikes have, but it's been so cold here in Atlanta it may be a month or so before I can report back on any improvements. I'll let you know what happens.