The air cut off valves can be blocked off with some rubber from an old tube. They help with emissions and blocking them is common practice. However, I have not done that myself yet just going off what I've read. There doesn't seem to be any adverse effects on performance and blocking them seems to help stop backfiring upon deceleration. Anyway we are all on tight budgets so I thought I'd mention it so you can save a few $$.
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