What could cause a 1980 KZ750 Kawasaki to crank slow like the starter is dragging but if you jump it turns over fine and starts?

1. Weak Battery: If the battery does not have sufficient charge, it may not be able to provide the necessary power to turn the starter motor properly. Check the battery's voltage and charge it if necessary or replace the battery if it's old or damaged.

2. Poor Electrical Connections: Loose or corroded connections between the battery, starter motor, and ignition switch can impede the flow of electricity and cause slow cranking. Inspect all electrical connections and clean them thoroughly to ensure a solid connection.

3. Starter Motor Problems: The starter motor itself could be faulty. Check the starter solenoid and ensure that it's engaging properly. If the solenoid clicks when you turn the key but the engine doesn't crank, the solenoid might be faulty. Additionally, brushes within the starter motor can wear out over time, causing sluggish performance. Inspect the brushes and replace them if necessary.

4. Engine Oil Viscosity: Thicker engine oil can make it more difficult for the starter motor to turn the engine. If you've recently changed the oil, ensure you're using the correct viscosity recommended for your Kawasaki KZ750.

5. Compression Issues: Low compression in the engine can also cause slow cranking. Perform a compression test to determine the health of the engine's cylinders. Low compression may indicate worn piston rings or other engine problems that need to be addressed.

If you've checked these items and the issue persists, it's best to seek the assistance of a qualified mechanic who can diagnose the exact problem and perform necessary repairs.