1992 40 hp miss

[baitbucket2]

I have a 1992 40 hp Force that starts, idles, and runs ok, but when I am running every so often it has a miss that will jolt the motor hard like it cut off and then instantly back on. It seems to get worse as the day goes on. I am concerned because it sounds like it is such a hard knock that I will damage the motor if I keep running it so I have stopped until I can get the problem fixed. The first time it happened I thought that I had hit something floating in the water, thats how hard the knock is. Any ideas?