2000 Yamaha 150 hp 2 stroke will not stay throttled up on plane , throttle backs off to 3000+ rpms a

I had this engine out twice in last week, yesterday powered up fine and stayed on plane. Today the same when I first went out in the morning. Coming in today it will come up on plane and run at 6000 rpm for about 20 seconds and powers down to 3000 rpm, will not power back up on plane? What could be wrong, no new fuel bought for last week or so, motor ran fine until today coming back from fishing.

When's last time you pulled carbs and jets? Doesn't take much gunk to clog jet. To rule out fuel pump, squeeze primer bulb when rpms drop. If rpms increase there's ur problem.

That's funny you ask about the primer bulb, the one on my 150 Yamaha will not pump up to where it gets solid? I have a 9.9 kicker on it and the primer bulb gets hard when you squeeze it. Another Idea I thought of to eliminate fuel is to hook the engine up to a 7 gallon portable tank I have and see if it will run normally. I try to keep the fuel tank as full as possible on this boat and its down to a 1/4 tank, if there is water in the fuel with the tank that low could it be pumping more water to the engine or does the water fuel separator prevent that?