Engine has been running great. Flew last weekend and then Wednesday was going to fly. Started up and it was sounding rough at idle. I warmed up a minute and advanced the throttle and it continued rough until it got to 3000 rpm. Let it warm up some more then ran it at 3000 rpm for a couple minutes hoping to clear up the problem. No joy. I ran it at high idle and turned off the fuel valve. After a while it smoothed out just before it was starved for fuel. Opened the fuel valve before it died and it ran smoothly for a few seconds before it began to run rough again. Sounds like a carb problem where maybe one carb is getting too much fuel. Mag check at 3k is normal. I dropped the float bowels and the floats looked to be floating normally. Fuel looked clean. I had run on this tank for a couple hours Saturday. Gascolator had clean fuel. Suggestions? Why would a good,running engine start running rough after just a few days?