I'm new to the boating community, but I'm not new to engines in general. Here's my problem. I have a 17' Key West with the Johnson 48 SPL '87 motor. Ideling everything is fine. When I go full throttle it starts to bogg down and the RPM's drop to about 3000. Every once-in-a-while it will sputter trying to gain RPM's but will not. If I hold the choke in it revs right up and stays around 4800 RPM. It usually will go to 5500 RPM full throttle. I ran old gas in it the first time. I have since then put new gas in. Should I suspect trash in the carb or the power pack?Thanks.