The carburetors on any multi cylinder motorcycle will give you fits if the bike has ever been sitting for a few months with gas in them and no stabilizer. There are rebuilders out there with very good reputations who will rebuild your carbs to factory new. It'll cost around ~$400 to $500.
Your best bet is to just download the rebuilding guide (DOHC carb cleaning run down -
http://honda-cb750-s.456789.n3.nabble.com/file/n685918/Honda_Carb_Manual_revD.pdf Alt link:
http://creativeconceptcomputers.com/CB750/dohccarbmanual.pdf) and follow it before giving up. The three biggest issues are dirty idle/slow jets (you've got to pull them out to clean them), leaking float valves (you've got to clean the seats really well), and leaking O-rings in the fuel rail between carbs #1 and #2 (you've got to split the rack and replace the O-rings).
It's a nice looking bike. You wanted it at one time so don't give up on her now
If you part it out, there's a guy on here who crashes his
a lot. He'll want your timing cover and the rotor thingy. LOL (inside joke).
89 VN 750A - Given to son-in-law
79 CB 750K-sold 3 May 21
78 CB 750K
77 CB 750K
77 GL 1000 x 2
77 CB 550F
Holton, KS, US