Which one, the 305 (AQ230) or the 350 (AQ260)? help us help you by posting every bit of information you can in the very first post the next time you start a thread. it should not be this hard to get information on your motor to help you.
with a properly maintained cooling system, a properly maintained ignition system and a clean fuel system, a clean carburetor and proper adjustment, the motor should idle all day long at 650 rpm
what is your temperature gauge reading?
can you put your hand on both risers? at an idle, they should be fairly cool to the touch (about 120-130F)
if you open your fuel cap, is there a sucking sound?