New NS40C problems

I have just recently purchased a 1985 NS40C the guy I purchased it said it needed a coil pack. I put the motor on my boat just to try it out and of course it started missing at full throttle. He told me that he had just had the carburetor serviced so I am assuming that he was correct in it needing a coil pack I just wanted some advice on if that is what someone else feels it could be. If so does anyone know where I can buy one? What confuses me is that it starts right off everytime, it has new plugs and revs up with no problems in neutral does anyone think it is not just a coil pack before I spend 100$ for a new one? Thanks Help is greatly appreciated.

Start with a factory service manual, available at any dealer, and do a thorough diagnosis. Just throwing parts at the motor would in theory find and fix the problem eventually, but diagnosing the problem is faster, cheaper, and more efficient. If you do need a siamese coil, it is available: 361060401M IGNITION COIL ASSY $88.23