i have a 1990 rx7 carb set up with a dizzy . I finally got around to trying to time it well somehow i get the leading mark lined up with the leading timing mark start it up put the timing gun to check it and all of a sudden the mark the the main pulley jumps way off the mark and the only way to get it back in time is pull the dizzy out and restab it but it never stays could that be my timing chain or should i just pull the front cover off to check the gears or is there a tension pulley that keeps it tight ?

 

There's no such thing as a timing chain on a rotary.

Have you disabled the vacuum advance?

Check the dizzy to make sure there isn't some kind of mechanical problem. Maybe the roll pin on the gear is broken.