Tach problems

78 kz650 c2 bike revs up normally but the tachometer wont read past 3500rpm. im assuming its getting stuck or something. You guys got any advice ?

Cable operated Tach? I'd remove the cable from the engine and then pull the inner cable out,clean it & inspect for broken cable strands and re-lube it, installing it back on the engine.

Got a cordless drill? Connect one end to the tach cable and the other to the drill and see if the problem is the cable or tach.

Best do what mfolks said first

I had a piece of one of the bulb holders come loose inside and jam the tach. I took the tach off. I cut the ring which keeps both halves together. I took the 2 halves of the tach apart and fixed the problem. I put the ring back in place using epoxy putty as glue and clamped everything until it set. I kept the gap in the ring facing inward so not noticeable.

I think Z1 Enterprises outsource tach restoration. You migh want to contact them either and check that option.