Power drop at high rpm

[EngstromNK]

The last time I went out I had been running at 4000 rpm for about 10 minutes when the rpm's droped to 3800. The boat felt like I had stepped on the brakes. I throttled up to 4400 rpm and it ran fine for a minute and then dropped again. I throttled back and it cleared itself again. This went on for about five minutes until I arrived at my destination. The ride back was uneventful. Should I start with the carb or fuel pumps? I have a '91 Yamaha 150.

Another piece of info. When I was pumping the bulb before starting it never really got solid. Then I noticed a sheen in the water around the engine.

Thanks,

Keith