I have a 1998 150 Johnson, and the motor has ran great the last 3 years I've owned it. But recently the motor once it is warmed up sounds like its loading up or not firing on all cylinders. It ran from the dock to the Pier 41 which is 5 miles like a champ at 4300 rmp's. But then it would loose power and pop and choke and die. But then would restart right up, but still no power! Little help...........been told "Power Pack" how can I be sure before spending $200? Is this common? Can I prevent this from occuring?