Help!!! 1982 70 hp johnson outboard bogs down after it warms up

I have a 1982 70hp johnson seahorse outboard. I have owned it for 2 yrs and never had a problem with it until now. It runs fine for about 20-30 mins untill it warms up. Then it bogs down and has no power. But still seems to idle fine. If i let it cool down a while it will run fine until it warms back up. I brought it home and ran it with the water hose and it seems to run fine. Any Suggestions and help would be greatly appreciated.

Have you done any maintenance on the cooling system ?----------Impeller , thermostat , poppit valves.--------Salt water or fresh water ??

No I have not since I have owned it. It is always been fresh water

Water pump impellers are the most neglected item on an outboard motor.----The fact is they should be replaced when they appear to be working just fine.

Do u think that could be causing it to bog down afrer it warms up

Run with a timing light and see if you loose spark on one or more cylinders.--------Look into the carburetors ( strong flashlight required ) at full throttle on the lake and see if you are loosing fuel coming up the main jet on one or more cylinders.-----Simple testing that costs no money !

If I'd hazard a guess, I'd say it's cooling system. They'll idle all day long with a weak or non functional water pump because of the oil in the gas. Does the hot horn sound when it acts up, or are you sure it's functioning at all? That would be my first guess is cooling system. Next would be ignition problem. I had one last year that would drop spark on number 2 when it got warm. The only way I found it was ignition tester on the water when the issue would occur. It was frustrating as hell locating the issue because the coils always speced out when cold. It was only when the motor got warm that the problem with the primary circuit showed up on a resistance test.