Surging with B&G VTwin With New Carb - Please Help!

I have a garden tractor with a B&S 44N777-0124-E1 VTwin engine.  When I bought this (second hand), it ran for about 20 minutes and then would stall.  Sometimes it would take a long time to get it started.  Started by changing the spark plugs (later the ignition coils) and placed inline spark testing on both cylinders - not a problem.  Changed the fuel filter, made sure the fuel lines were not blocked and flushed the gas tank and then bought a new gas cap (no vapor lock).  Removed carb and initially replaced with an aftermarket Nikki.  Noticed that the intake manifold was warped - originally sealed with Permatex but later replaced intake manifold with new OEM.  Since I have bought a new OEM Nikki carb and still had issues with surging - only seems to have worsened.  I then decided to rebuild (new o-rings, gaskets, etc.) and clean my original Nikki carb - found that the o-rings on jets were loose and several ports clogged...did a deep clean with cleaner, drill bits, wire, etc.  Replaced and it ran better for about 10 minutes and I was able to cut the grass until it stalled again.  Continues to stall.  I'm now planning on adjusting the governor (springs seem to be okay) - but will reset.  Also, I plan to check gap on all 4 valves and reset back to 0.005".  After that, I'm at a loss - fuel solenoid works, has gas in the bowl, don't see an vacuum leaks (with starting fluid).  Wiring okay (no shorts), ignition seems okay.  Any ideas?  They are appreciated!

No fuel pump - this is gravity fed only since the gas tank is right behind the engine.  Every time I take off the carb - I have fuel in the bowl.  I've test the fuel solenoid and it works...plus if I had an ignition or short to ground, I would lose fuel immediately with the plunger plugging the emulsion tubes and the engine would stop.  This seems to run for 10 minutes and then surges for 30-60 seconds and then stops.  Seems it is getting fresh fuel.  

The surging is a symptom of running lean, running out of fuel  .
 
What does the spark plug look like when this happens, (turning it off immediately)?
 
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Pulled off the valve covers on both cylinders - 0.005" on intake and exhaust valves at top dead center (compression) on both - perfect (spec is 0.004 - 0.006").  Governor set all the way clockwise on full throttle.  Spark plugs are new (less than 1 hour) - they were clean and looked new.
 
I have a hard time believing it is fuel - i.e. running out of fuel...carb bowl is always full (1/4 cup or so) - I can see this when I pull off.  Fuel solenoid obviously works (hear click and can test with bowl off and visually confirm).  Don't see a short to ground (wire insulation good all the way back to ignition) and if 12V loss to solenoid, this would not take 30 seconds to die - it would die immediately with plunger plugging orifice to emulsion tubes.  
 
Pulled the carb again.  Going to put on new fuel lines to make sure I'm not getting crap.  
 
Yes - brand new OEM Briggs Carb (792295).  New OEM intake manifold, new OEM gaskets...air elbow original but seals tight.  Breather tube looks new.  Acted worse with this carb - it looked like the jets were flipped from the factory.  My understand is that the left (when looking from tractor seat) jet is slightly larger since this cylinder is mounted lower than right and must run richer.  Verified with micro drill bits.
 
Thanks.

Also...Not sure if a blown head gasket would cause what I'm seeing.  I understand the symptoms of a blown head gasket to be: 1. Noticeable oil everywhere, 2. Crap on the Spark Plugs, 3. Gas in Oil and smoke coming from dip stick, 4. Black smoke from exhaust.
 
The only oil I have is on the right cylinder underneath (dried, not fresh, mostly black dirt)...nothing collecting underneath.  Spark Plugs clean, don't notice any smoke rising from dip stick and the only black smoke is infrequent when first started (none otherwise).
 
Not sure it is worth pulling rods, and head to get to that gasket since not sure it would cause what I'm seeing.
 

Thanks for your help.  
 
I've got it all torn apart - including the carb.  Plan is to put that back together along with new fuel lines after flushing the tank (again).  Waiting on new valve cover gaskets after checking those.  Hope to have it put back together soon.  
 
Once together - I'll give it a shot with carb cleaner and then pull the plugs just after.  They look clean to me know.
 
Would be nice if this forum allowed me to post pictures. 
 
Regards.

Go to Post Images :  https://postimg.cc/files 
 
Open a free acct, upload your pic's.  Then copy and paste the "Hot link for forums".
Paste that here.  Your pic will then post..

Sorry for the late reply - I think I invited the devil into my garage with this one.  I put it all back together only to put gas in in and quickly discover a leaking gas tank.
 
Got it back together today - choked it and it start up and died after about 5 seconds.  Started again and it died even faster...now it won't start at all.  This is what I did:
 
1. Checked valve gaps and found to be at 0.005" on all 4 .  inspected spark plugs
2. Replaced valve cover gaskets
3. Rebuilt carb - all new o rings, gaskets, blew out all holes passages with cleaner and drill bit & brushes.  Jets clean - larger jet on left) and small air passages clean.
4. Put carb back on with new intake manifold and new gaskets - was very careful not to over torque long bolts as I know this can be a problem with gaskets warping
5. Adjusted governor - it was already all the way clockwise on full throttle
6. Flushed gas tank - new fuel filter, new fuel line, new gas cap, brand new gas.  Fuel filter full of gas.  
7. Inspected wire to fuel solenoid - no shorts to ground that I can see.
 
No idea why it will not start now - flywheel just turns but won't turn over.  I'm going to play with it again later this week but figured I would post some pictures.  Thanks.

Try un-plugging the oil switch on the engine.  If that switch is bad, it may be killing spark.
 
You may want to disconnect the thin, Black kill wire going to the coils. 
 
Again, your going to have to check for spark at the plug, 
spray some starting fuel down the carb throat and see if that helps
 
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Just disconnect it from the switch.  It's a safety switch  that'll kill spark if it doesn't see oil pressure.
 
Disconnecting the wires at the coils would do the same thing but we're trying to narrow it down..
 
The oil switch may very well be bad, they do fail... 
 
Also, can you feel/hear the carb solenoid click when the ignition is turned on and off?
 
 
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