A Different Surging Twist

I have read many threads on Honda engines surging.
Most seem to occur when the mower is new or cold.
Mine is a bit different.

Engine is GCV160A Type S1M and GJAE series. Automatic Choke, BB65E A carb.
It starts and runs fine for about 5 minutes, then the surging begins.
Most things I have read indicate that the choke should open within 3 minutes.
As I live in the South, I would not think that it would take 5 minutes to open.

I have replaced intake gaskets and cleaned the carb 2x.
May have seen a bit of an improvement, but still surging.
If I turn off the gas line valve, it continues to run (and surge) for a couple minutes, so supply and gas tank problems ruled out.
Air cleaner is new; spark plug darn near perfect.

I did not give the carb a full soak, but made sure the main jet, main nozzle and pilot jet were all clean,
and blew air thru as many passages as I could see.
No air needle on this one.
Obviously I have missed something, but what??

Thanks.

Maybe the third time was the charm...
As it is a rainy day here, I decided to take another stab at the Honda.
This time I ran the stripped carb thru 3 cycles in the ultrasonic cleaner.
Sprayed with carb cleaner, blew off/out and reassembled.
Ran for 10 minutes without skipping a beat.

Thanks to all who read the post............