At the end of last summer the motor began to idle very rough and often stall at slow speeds - ran fine at higher revs. This spring I had plugs and fuel filter changed. First time I tried to start the motor, it refused. After spraying starting fluid into the intake area it started immediately. Then after approx 20 seconds it would run rough again until I sprayed more starting fluid - then would would run parfect. After getting it into gear and throttling up, it runs fine - when I back down on the throttle it quits. Any ideas?<br /><br />Engine is four stroke - 1999 w/about 200 Hrs.