engine keeps popping out of gear

[<Mark Watford>]

Recently purchased a 6 hp yamaha around 1995-1997
was told that the lower unit had been worked on and parts replace. The engine runs fine but around half throttle you can hear the engine popping out of gear. The shifter doesn't move. In reverse at 2/3 rpm it comes out of gear entirely. Took the I guess what would be called the gear carrier out everything looks new, noticed that the pin at the end of the assembly had the flat side out on the other side it is rounded put it back together with the rounded side out same problem. Any suggestions or what I could check next.

Thanks

[<boats.net>]

Take the parts to your dealer they can tell you what parts are needed