Recieved this boat from my grandparents who didn't use it anymore. Sat for 3 years in the garage. the motor is a 1985 60hp Mariner. Ran great for the most part. This Spring I took it out and it would be ruinning and then all of a sudden it would jerk and then die. It took some time to restart but would start. It would idle fine but when I would put it into gear it would starting to jerk again. I had it in the shop and they fixed the CD box. Took it out and it started right up and sounded great! But once I got to about 1/2 throttle it would bog down and if I didn't feather the throttle back and put it into neutral it would kill. I let it sit in neutral for 5-10 seconds and I would be on my way again until I got to about 1/2 throttle. Any ideas as to what the problem is????