Having problem getting Suzuki Katana 600 to idle properly after starting!?

After starting Suzuki Katana 600 and releasing the throttle grip the motor continues to race even though the throttle valves are closed.. Sometimes it slows and sometimes it must be shut down. We have replaced the throttle cable The throttle cable connections and routing seems to be OK. The idle mechanism appears to work properly. We have just recently replaced the carburetor and gas tank (Calif emission type).