If they have a molded in velocity stack that is a better design and closer to the original.
The bike will still need slide needle repositioning and re jetting. Possible idle jet change also but check with others that have done the same mod and save yourself time and money.
You cannot just change the main jet only and expect for it to work correctly.
The main jet controls WOT and a little crossover from 3/4 throttle thats it.
With the Carpy's exhaust and pods I would lower the clip needle one notch.
Increase main jet size and if the idle is too high or it has any hesitation when giving it quick throttle then the idle jet may need to be increased.
The stock main jet was 105 , I would change that to a #115 or #120.
The needle clip position was 4th down from the top stock.
The idle jet was #40 ,I would change that to a #42 if the idle will not come down or it has hesitation when giving it throttle.
Do not baby the throttle when testing.
I would move that needle clip down to the 5th groove from the top if there is any hesitation at all.
The "F" model was very stingy on gas to start with.
You said, "CB750F1" . Most charts just have CB750k/F listed.
Another member of this forum "Bryce" has a 1975 and has a similar set up.
Talk to him.
I do not have records on other 1976 CB750F owners.