I have a 1978 Cb400TII that I've been working on trying to get it tuned up after it was given to me by a family member. The bike has 24K miles on it and has not been sitting so any long period of time, it was used pretty regularly before I had it. The engine runs well by my standards, this is my first bike so I'm not too experienced in that regard. It will start right up and doesn't really get bogged down through the gears/RPMs. The issue I seem to be having with it is that the speed tops out at about 55-60mph, and from what I've read online this bike should get up to 80-90mph. I did a compression test and it was about 150psi in each cylinder. I also did a leak down test at TDC on each cylinder and found less than 20% leakage. I've seen that the sprockets could be changed out but my front has 16 teeth which I think is stock. There is what I think to be a small leak in the head gasket as there is a small amount of oil that is around that area I just haven't cleaned it off yet to see f its leaking out or not. I'm not really sure where to go from here so hopefully, someone can advise on what to do to bring the speed up.
Other things I've done to this bike since getting it.
changed the oil (Delvac 15w40) and the filter,
changed the brake fluid and adjusted the rear brake
adjusted the clutch
Cam chain adjustment,
cleaned and lubed the chain,
cleaned and reoiled the air filter
cleaned/adjusted and Synced the carbs
replaced the battery (AGM battery)
adjusted the slack in the chain