stumped by this gx390 issue

Hello.  I’ve worked on these honda engines for 20 years, as all my biz equipment has some version of the honda.  This time I am stuck.  This GX390 is showing every symptom of a carb issue, fuel, or air leak.  However, that is not the issue.  “hunting,surging” and appearing to be running lean. I’ve tried 5 carbs, checked for air leaks, ran a new fuel source, adjusted the gov, even replaced spark plug.  Seems like it would be a simple carb issue but I even removed another from an identical engine…same exact result. About ready to replace the whole gx390 engine.  Any ideas?

Different jets

Some things to try:
 
I gather you checked fuel flow to the carb, no restriction from the tank?  Or past the fuel filter "bowl"? 
 
Loosening the fuel cap (while running) to rule out the fuel tank creating a vacuum and not letting fuel flow?
 
Did you try spraying carb cleaner/brake cleaner all around the intake area, checking to see if the cleaner was sucked in and made a difference in running temporarily?   
 
Perhaps a hairline crack in (if equipped) the heat/manifold (between the head and carb)?  
 
Putting your original carb and manifold on another engine and see if it acts up? 
 
.

Well, I think I will give it up.  Guess I will take it to a honda small engine shop.  Spraying started fluid all around the carb didnt really show that it sucked any of it in, and didnt change the engine behavior.  Replacing all the intake, plastic, and gaskets didnt show any change either.  I took off the valve cover gasket for no real reason...all looked fine with the seal on there, and the 2 valves looked normal to me. 

I may try something else first.  Would the gov counter weights being gunked up cause this issue? might try putting little seafoam in crankcase