It is unlikely that this is a vacuum related issue.
The description you give indicates problems at the pilot / slow jet. When the bike runs only
with the choke / enrichening lever pulled out, you have one or more jets obstructed by gummed or varnished fuel, or a possible "floater" providing blockage.
This can be intermittent. My first step would be a chemical attempt to cleaning the jets. A high dose of Sea Foam, Chevron Techron Concentrate Fuel System Cleaner, [not Pro-Gard, it's weaker little sister], Berryman B-12 Chemtool Carburetor and Choke Cleaner, or your favorite Witch Oil. [I like the Chevron] I would begin by draining the float bowl, pulling the fuel line at the petcock, and dumping in a 50 / 50 mix of gas and carb cleaner into the fuel line. Reinstall the line to the petcock. Add a strong dose of cleaner to the fuel in the tank. You are trying to correct a problem, not prevent a problem. Use a stronger dose of cleaner. Start the bike, and using the enrichener as little as possible, rev the engine a bit and shut it off, letting the jets soak in the cleaner for a few hours. After allowing the chemicals to work, start the bike and run it in the lower RPM range as much as possible, as that is where the blockage appears to be. While it seems a little inconvenient to perform this chemical treatment, it beats rolling the carburetor over and pulling the pilot jet, which is what you may be doing if the chemical jizz does not work.
If it comes down to a manual clean job, this is what you are looking at:
Bottom of carburetor, with float bowl and float removed.
Be careful not to strip or break the small pilot jet when you try to remove it. It may be necessary to grind the end of a small screwdriver to fit the jet just right. Even after soaking, the jet may still be plugged. Do not rely on visual inspection of the jet to determine that it is free of obstruction. Use a small "E" guitar string and push it through the jet. (A wire strand out of a wire brush may work. The wire brush should measure about .013" in diameter.) The smallest jet drill you can get is #80, which has a diameter of .0135". You can use the wire and not enlarge the hole, at least not by much. Some manuals say not to insert any wire jet cleaning tools into the jets. However, Honda and other manufacturers produce them as special tools for the dealer technicians. I find Brake Cleaner works well for jet cleaning ONCE THE JET HAS BEEN REMOVED FROM THE CARBURETOR.
Don't use Brake Cleaner in
This cleaning process can be done without removing the carburetor from the bike. It will require you to be patient and careful, however. Not a good project fro those with ADD. There will be no adjusting to content with. You will reassemble what you disassembled. As long as you lose no parts, remind yourself that no large amounts of torque can be used on a carburetor, you should be OK.