Call Kohler and ask for the high flow valve. I seem to remember it comes with a low flow one. This did the trick for us and we're on well water (low flow anyway). For less than $20 you should be set.

I have the Karbon and yes, call Kohler, they are very responsive. If anything, my Karbon is a tad too forceful.

DH says its an aerator not a valve.

When my Karbon was installed the water flow was 'limp'. I was so disappointed. My plumber took an hour and took the whole thing apart, took each section and blew into it. Finally I called Kohler while he was there and the last thing we hadn't checked was the last section with the spray button. They said to push the button in, take off the cover and check those parts. He blew into that and a tiny tiny piece of red plastic shot out. After that, everything was fine and the pressure was strong.

He also had taken the faucet off the base, put a cup over the hole and turned it on to make sure the water was coming out at pressure. That way we knew the water was coming at pressure but there was something in the faucet itself that was blocking it. Good luck! We love our Karbon.