I would check the basics like compression and oil pressure, also ignition timing and timing advancer. A timing problem can make you have to crank the throttle open to get any power. If the basics are all good: does it have stock pipes and airbox? Messing with those can really hose up the tune. If it turns out to be just the carbs, that's fixable.
Agree to check the diaphragms for any slits or leaks. If those are even slightly leaky, it can screw the running up horribly. Guess how I learned that....
For the fuel system, start at the top: clean the tank and petcock, install inline filters, clean the carbs really well, check intake mounts for vacuum leaks.
1979 KZ-750 Twin
