Tape punch

I'd posted here a while ago looking for info on a Tally 420PR tape punch and have built a driver board to interface it to a PDP-8A. But there is a problem with consistent punching/feeding (the result is often a longitudinal tear instead of holes) even with the pulse widths set to the recommended 4.5 ms +- 0.5 ms, -24 volts, and the feed mechanism intermittently binds up too. Currently I'm running it with only the sprocket and feed drivers hooked up, and simulated punch commands from a 555 timer, so the result should be continuously feeding tape with just sprocket holes punched in it. I suspect the problem is that the feed pulse starts immediately on the falling edge of the punch pulse, so the pin hasn't cleared the tape as the feed mechanism starts to move. It also tends to stick in that position with the tape not moving (you can hear the solenoids buzzing but the feed sprocket is not moving until tweaked backwards a few degrees by hand). According to the schematic, the escapement solenoid (which allows the tape to feed one row per pulse) is supposed to be actuated internally by contacts on the feed solenoid so there shouldn't be a timing issue there. Does anyone have more info on this punch model, or experience with these asynchronous mechanisms in general? Is there a requirement for a delay between punching the holes and pulsing the feed solenoid? How long does it take for the pins to move up or down after drive is applied/removed? thanks Charles