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Hi everyone. I have a 1977 KZ750B (twin) i am currently undergoing a new starter clutch after the engine became seized at idle luckily. The bike needed a head gasket so i have the top end tore down. I was using carb cleaner to clean all the carbon off the pistons and head. I sprayed carb cleaner in the head (with it off to remove carbon buildup) the right side valves were tight they held the carb cleaner. The left side had slowly drained the carb cleaner. The bike has 15k on it. The carbon build up on the valves seems to permanent (carb cleaner and a brass brush will not remove carbon).  My question is with the motor locking up like it did could that have caused one of the valves to bend? I am thinking it just needs the valve seats cleaned up because the amount of carbon build up in the combustion chamber was severe. I will attach pictures. If you have any questions for me to help you help me better i would appreciate it. I have done many engine rebuilds but ALWAYS sent the head out to be rebuilt. I would like to get in there and fix it myself. I Know that if the liquid is leaking out then compression is most definitely.

Most of the time with a low mileage bike like that if you pull the valves and clean and them lap them into the seats that's all that's needed (other than new valve stem seals and valve adjustment shims).  If in doubt post up some photos after you get the valves all pulled and someone will chime in.

Full Valve job runs $189.00 plus parts.  www.aperaceparts.com/cylinderheads.html

You asked about bent valves. The answer to that question depends in part on what caused the engine to seize. If the cam chain broke, or a chain guide or the tensioner broke, allowing the chain to jump a tooth or three, then there could have been some valve to piston contact, resulting in bent valves. Were there any marks on the piston top suggesting any contact?
If there was a different cause of the seizure, then that extreme carbon buildup is likely the cause of the leaking valves. Old, hard valve stem seals can leak a surprising amount of oil into the intake ports, resulting in serious carbon buildup, and valve problems.
At the very least, I reckon the head will need new valve seals, some light lapping of the valve seats and a thorough cleaning. Maybe more. Lapping and new seals is perfectly doable by the average dude with basic skills. More than that probably should be left to an expert. A reliable shop like APE, Restcycle or Cavenaugh would be a good choice.

That's right. My valve guide seals were leaking so bad I was fouling plugs every 200 miles. When I finally took the head off to install new valves, the old ones were seating on the carbon. I expected to gain clearance but after lapping I lost most of it. I had to use the smallest shims available. The intakes were fine. Here we are two years later and I had to "tip" the exhaust valves to get back to the center of the adjustment range. I'm looking at a complete rebuild next time. Valve guides, seals, three angle seat grind, the works.
Steve