Troy-Built w13.5 Briggs hunting and backfiring

youtu.be/pFrINtBDve4

Do not know the model but I posted pics that might help.
 
Just started three times and no backfire. Maybe extra fuel that has evaporated. 

Will do as you suggest and report back in a bit.
 
Appreciate the help on this. 

"Surging is often related to a lean condition..
 
First, spray brake or carb cleaner around where the intake manifold bolts to the carb AND to the block
(and to the manifold itself).
See if there's any noticeable running issues.  We're looking for an air leak.
 
A visual inspection of those two 0-rings wouldn't hurt as they tend to flatten out and not seal..
 
There's an o-ring style gasket on both ends of the manifold and if it's leaking WILL cause 
the surging..
 
The back firing could be several things.
      Excess fuel, timing off, valve being open."
 
B&S Model 21B807   13.5 HP 
 
First:
 
I did re-adjust both valves to .005 for both intake and exhaust. Did this a week or so ago.
 
I again removed the carb and again did a cleaning on the bench. Ran wires down every hole I found, placed the carb in my ultrasonic cleaner and air dried it all. Even popped off the silver cap for the air/fuel mixture control and cleaned in there. Replaced with new cap. Put back together. No change in surging whatsoever.
 
Next:
 
Spraying carb cleaner around the carb area I got a smooth running engine when I sprayed between the output of the carb and the plastic manifold. I removed the carb and added non-hardening gasket maker to both sides of the (new) gasket that was there. Put back together. Started up and no change. Still surging. Did notice if I sprayed again engine went calm so I removed the carb and found most of the sealant was gone. Blown or sucked out by the engine.  
 
So, I'm now inclined to redo the gasket but using RTV sealant and waiting 24 hours for it to cure.
   
Question: is the carb cleaner working by sealing off the air leak or is the spray just feeding into the fuel mixture and doing the smoothing that way?