1) check your carb base gasket, unbolt the carb and retorque to around 10-12 foot pounds, if you over tighten a carb you can cause the base to bow slightly and cause a vac leak.

2) reset your idle mixture screws to 1.5 turns. if you rebuilt the carb you changed the little cork gaskets around the needle screws.

Adjust throttle screw to keep engine running so you can work on it

3)get an assistant, and a bunch of rags: put the rags around the carb base open the primary fuel bowl sight screw if fuel comes pouring out you need to lower the fuel bowls, drop the level with the adjustment nut and tighten them up, start the motor and have your assistant watch the sight hole if fuel is still pouring out, cut the engine and readjust, repeat as necessary. and do the same for the rear bowl.

secondary’s open under engine load, you won't see it engage revving the engine in neutral or park. 

if you rebuilt the internals correctly, changed all the gaskets and replaced the power valve, your problem should just be adjustments, of the carb.

you can fine tune the idle screws with a vacuum gauge
your aiming for max vacuum at your desired idle speed. or you can close down each idle screw until you hear the engine rpm drop by 200 then back off 1/4 turn

you can confirm your idle mixture screws are not leaking by closing them all the way the engine should stall. if not, you could have a stuck butterfly or another leak in the idle circuit

finish up by re adjusting the idle as needed.

Help something helps. I know what it is like to chase something. Do you know an old an school car guy that a six pack of beer may get them over to take a listen. Sounds like you are close. 

Good luck, If I can help let me know.