Check the timing chain or gears for slack.
1. timing mark (the ball on the flywheel) on its mark (the needle inside the hole on the bell housing).
2. remove the distributor cap, leave the rotor in position.
3. Mark the position of the rotor with paint or liquid paper.
4. turn the engine with a wrench and at the same time look and the rotor. when the rotor just begins to move stop turning the crankshaft.
5. make a mark on the flywheel where the pointer is.
6. turn the engine backwards untill the rotor just begins to move.
7. mark the flywheel again.
8. measure the distance the fly wheel moved from both marks you made.
If that distance is more than 10 degrees then you have valve timing problems. ie: timing chain or gears as the case may be.
