I have a 16 horse power Briggs Vanguard V twin over head valve #303447. This engine has about 3000 hours on it and has run great for the past 2999 and has been very well maintained all its life. Recently it lost power and started blowing blue/black smoke out the exhaust. This condition has gotten MUCH worse, its smoking so much now that it fills a three car garage in under a minute. It now only runs under full choke and has little to no power.
I then replaced the carb with a new one, new plugs sparking fine, oil changed, two new head gaskets, fully inspected heads and valves, compression checked out to about 110 psi on each cylinder cold, air filter good and clean, new intake manifold gaskets, new fuel pump.
After doing all this the engine STILL does the same thing. Only starts up and runs with full choke at 50% throttle or more, smokes like crazy, and still has no power.
HELP ME PLEASE.

Anyone?? Any and all ideas are welcome

It actually sounds to me like it could be bad piston rings and you are getting oil blow by in the cylinders.

I had thought about that but I'm still getting good compression. Thanks for the advice , any other ideas?

Check your fuel pump , check the line going to the engine from fuel pump for leaks,
Check for leaks at intake gaskets on engine to manifold,
Make sure your getting good flow from tank.
Luck

What DG says and try removing the gas cap.

Thanks DG and ballengerb1, I believe all of these are sound logical ideas as well and have looked into them: the fuel pump is new and checks out as well as the fuel filter, I can't find any fuel leaks anywhere, the intake manifold gaskets were replaced with new ones when I did the head gaskets and don't appear to be leaking. Any other ideas or trouble shooting tests I could try before I bite the bullet and tear it down completely

Have a cylinder leak down done .
This will show if valves are leaking or if its leaking by the piston rings.
This might sound like a stupid question , but its not . Do you have any Oil leaks ? What was the valve clearance at ?
Luck