96 bombardier 717 twin jet boat speedster 5894

[Nicholas]

(Just lube the engines.) Took it out it run ok for about 15 mins. And then i lost power. Rpms were about 4.It will try to get up and go and then it looses power.At times it seems it was picking up speed and then it looses speed and it slows down. I checked the propulsion and drive system it seemed all good but when i put it in full throttle it will idle up and loose power and stays about 4 rpm and at all good times it at 6 to 7 rpm when its running good. What should i check first? It didnt do this tell i lude the engines.