Thumping when accelerating

[steplift20]

I don't know how to adjust the cable but I feel like that's your problem. I had a issue like that years ago only in reverse ,I brought it back and Jimmy from anglers marine who was a great mechanic adjusted it on land but said if it still happens to bring it back and thank god it didn't happen but he said the adjustment is very small so I can see you not getting it 100 percent right but I
would bet that's your problem