If I recall correctly (1975), 6-7000 was all my 750 tach would read tops, on my 74 CB550. I don't know what stopped it from revving; Valve float or point bounce. But it saved itself from blowing up, as I left the throttle wide open with no load on it, frustrated I couldn't get to red line... The wrecked bike had the original dials smashed. Bone yard sold me 750 replacements.
I didn't know at the time that the 750 tach ratio was different than the 550 tach ratio.
With a 550 tach installed, it easily made it to red line. Dooh!
I still want to see your spark plug deposits with a plug chop done when the engine tops out. If too lean, there will be lack of deposits, If too rich, the tip insulators will be coated with carbon. The plug tips are your window to combustion conditions inside the motor.
You don't adjust the airscrews for best idle. (I've tried that.) That will just make the power response off idle under load dismal, as you don't have accelerator pumps on the carbs. The idle has to be a bit overrich for when the slides are lifted and there is and inrush of air and simultaneous drop in carb throat vacuum (which is what is drawing fuel though the fuel jets), the carbs go over lean, no power.
When I adjusted the air screws for best throttle response under load, low and behold, the air screws were right at factory setting. Of course, my bike had stock induction and exhaust on it. So, smack your forehead, what do you know, factory setting worked best.
I once had a 75 CB550 with a Mac 4 to 1 and Foam pods on it. A wanna be cafe racer, where I methodically reversed most of the mods that made the bike painful to ride on the street. With 022a carbs set up in stock configuration, it ran well and fast at all throttle positions. FYI
Yes, I checked all the carb internals and measured to be sure they weren't altered away from what their markings reflected.
Cheers,
