I have a 2000 Suzuki DF25 4-stroke with an idling issue. It seems that when I start it up it idles perfectly until it heats up at about 3-5 mins. It then starts to idle very rough. I give it gas and it smooths out and no issues running, just at base idle it sputters. Sounds almost like an ignition issue. I pulled the plugs and they are clean. Any suggestions?