First off, we need to know "which" carburetor you seem to be having issues with. In this forum you will find definitive info regarding nearly every carburetor that was used in ihc light line vehicles except for the carter thermoquad which I've not yet done, that one is in the mill right now.
And we need good pics of multiple points of the top of the engine so we can see your set up as it is currently.
I don't wanna blow out a bunch of "maybes" here without knowing exactly what you have.
If the choke has to be wired shut in order enrichen the mixture enough to run, it can't be runnin' worth shit!! And a vacuum level with the choke closed means nothing. Let's stay away from using terms such as "about", "kinda", "good vac", etc. If instrumentation is being used, we need exact numbers.
Blowing black smoke simply means an extremely "Rich" combustion chamber condition exists, again, created by having the choke plate closed in order to run.
As for the electric fuel pump you refer to marketed under the "mr. Gasket" brand name, it must be the lower pressure range version. The packaging will state the range, which iirc for the lower pressure mr. Gasket pump is 4psi>7psi. All oem-design Holley carbs are designed to use a standardized fuel inlet pressure of 5.5psi so if that is the one you have installed, it will be ok, if not, then you must use a fuel pressure regulator.
In many threads that have been started in this forum, root cause of drivability and performance issues lie in the ignition system. The ignition system must be in perfect condition overall and at each component level before dealing with any fuel-related issues.
Carburetors generally don't "wear out" but can be heavily damaged by engine bay fire, neglect (fuel deterioration), and corrosion (internal moisture contamination), and in nearly all cases, it's a combination of at least two of the three on this old junk that as been sitting. Along with heavy deterioration of the entire fuel storage and delivery system. IH stuff is no different than any other vehicle in this respect.
Most all of the "rebuilt" carburetors still available through the chain parts houses are crap, most especially anything with the "champion" label (not the same as champion spark plug brand)! I "rebuild" a "rebuilt" someone sends in nearly every week! That is exactly why ihon has available new "conversion systems" for updated carburetors that work well on some IH applications.
No doubt we can make yore rig play nice, but we must have definitive info regarding your particular set up, not someone else's or whatever "from the factory" was! Then we'll proceed in a logical progression of diagnosis, around here...shot guns are only used for bird huntin' and home defense.
