What could be the cause of bad compression in one cylinder of my katana 750?

1. Head gasket. 2. Hole in piston (no compression) or rings failure (low compression). 3. Burnt valves/badly adjusted valve clearances. 4. Cylinder head cracked. But before you rip the engine apart, try these: Head gasket, run the engine and brush some soapy water in the gap between the head and the barrel and look for bubbles, they will be big. Rings, take out the spark plug and check the compression. Squirt in some oil and re-check the compression. If the compression rises, it's rings. slacken the push rod adjustment/ remove rods so that valves do not open. Check the compression, if still low it's valve/ head failure.