I just purchased a 1966 Johnson 3 hp. The seller ran it in a barrel for me and it sounded pretty good. Before he started it, he tapped the top of it with his fist a couple of times. I got the engine home and put it on my boat. It wouldn't start so I tapped the top like the seller did and it started. I'm assuming that something must be loose inside but I have no idea what to look for or what may need to be replaced. Any help would be appreciated. Thanks in advance.