Mid run power problem 1985 60hp

[ORLANDO85WHALER]

I have a 1985 mercury 3 cylinder outboard. After thirty minuets of running it bogs down to les that half power. If I shut down for one or two minuets it runs fine again. I have already rebuilt the carburetors with new kits, put in new coils and plugs, new impeller and fuel pump. Any Ideas would be greatly appreciated.

Thank you