Miss after warm up

[Homer31]

I've got a 25 year old "mint" Toro Personal Pace walk behind. It has the aluminum deck & premium 6.5HP engine.
It starts on the first pull after one prime pump and runs perfect ...for awhile.
After warm up it starts having a mild miss that continues until I shut it down.
I've replaced the air filter, spark plug & magneto. I've pulled the metering valve out of the carb & insured all passages are clean.
It's not a big deal as it cuts fine & does everything I ask of it, it just has this miss while using it & it is not totally perfect.
I am still missing something (no pun intended).
Any ideas?

Thanx - Bob

 

[Auto Doc's]

Did you set the airgap between the coil and the flywheel magnet? A simple business card will work. Also make sure you have the correct plug for the engine. Not just any plug will do.