I was out on a river yesterday with my 60hp 2up. Ran fine for about a half hour, then I shut it off for ten minutes or so. I started it and it idled and ran to about 2500rpm fine, but anything above that it sounded and ran rough. Full throttle was about 30mph, I didn't have the rpms up and didn't want to run it again. It had this awful rattling noise. I shut it off and started it again and had the same problem. I idled to the nearest beach and looked in the drive and didn't see anything. After sitting for 20 minutes it started and ran fine. I took it back anyway and I'm not going out on it until I get it resolved. I checked coolant and oil and everything was fine there. Any ideas?