Hi, I am a new baot owner. My new to me boat is a 91 hydrasports with a 140hp johnson outboard. Took it out for its first test run and the engine idles a little rough but cranks right up. When running it sounds good but will no go faster than 8 mph. When i throttle up the rpms seem to go up but the boat will not go faster. I believe it feels like it is bogging down. The engine will never die out though. What could be the issue? Take it easy on me as this is my first boat and am only partially clued in.