I bought my first bike a few years ago, a 1981 Kawasaki KZ440 LTD. When I bought it it only ran on one cylinder and had carb issues. Since then I have rebuild the carbs, changed the oil, readjusted the valves, and fixed all wiring problems (all were minor). The bike has ran like new for a while, and has made me very happy, but recently I have noticed that while in 5th and 6th gear the bike won’t excise 5500 rpm, and won’t make it over 60mph. 4th gear makes 60mph at around 6500 rpm easy, but as soon as I shift into a higher gear, the bike seams weak, and wont exceed into higher speed or rpms. I have readjusted my valves and tuned the carbs, but the bike is still having the same problem. Torque and horsepower seem fine in the lower 4 gears, but once in 5th and 6th power seems to be weak. I’m an thinking it maybe be either the clutch slipping or possibly the piston rings losing compression under load? Though I would love to hear someone else’s opinion before tearing the bike apart.