Putting your hand over the intake like that, is the old-school/poor-man's manual carb choke. You shouldn't have to do that if everything's working right. There's a shot in The World's Fastest Indian of Burt (Anthony Hopkins) doing this at the start of the film when he's starting the bike. Nowadays (ie the last 38 years) we just yank on the choke lever. Needing to do this is, imho, a symptom of dirty carb jets.
Regarding the brakes, if tapping them freed them up, but they tightened up again when you used the brakes and won't let go, that says to me that the pistons aren't retracting into the calipers properly. This is usually due to bad caliper piston seals.
Fortune cookie #1 say: "I see carb cleaning in your future, followed by syncing feeling."
Fortune cookie #2 say: "Replace caliper piston seals to unbreak brakes."
Fortune cookie #3 say: "You can tune a CB750 but you cannot tuna fish, so tune up your CB750!"
Seriously though:
1. Clean carbs.
2. Change oil
3. Cam chain Adjustment
4. Valve adjustment
5. Timing adjustments
That will probably get you up and running unless there are deeper issues. Then,
6. Carb sync
7. Brake overhaul and fluid replacement
8. Inspect wheel bearings
9. inspect swingarm bushings
10. Lube or replace steering head bearings.
11. new tires (probably)
12. New chain (maybe)
That will cover the basic safety items.
Do post some pics when you get a chance.
cheers
mystic_1
Edit: +1 to Hush, old gas goes bad. Replace.
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