84 K-5 4 bbl carb. Set timing at 5 degrees - tightened the distributor while the engine is running - checked timing and it was still ok. Tugged on distributor and it didn't move and the timing was still ok. Shut the engine off, restart the engine and the timing has moved anywhere from 5 - 8 degrees. The engine has new timing chains and gears and new distributor. I can't figure out why the timing is moving. Can anyone help?

 

worn distributor gear, sticky vacuum advance, vacuum leak, timing checked at different idle rpms.

 

If u put a roller cam in it you need a cam button to keep it from walking and causing eratic timing