While not that familiar with the D2 model, I do know on the larger tractors of the same era, there was as specification for the adjustment, in the serviceman's reference book about how far you turn the screw = the amount of centrifugal force to release pinion gear. There is a sweet spot and you certainly do not want the diesel to overspeed the starting engine. It may be wise while playing with the adjustment to make sure you can shut the diesel off quickly or disengage the starting engine clutch. I would think the latter should be possible, but if not you can take the air filter pre-cleaner off and use a small piece of clean 1" board to cover the hole, cut off air, it will stall, same for a runaway diesel.
I saw the tractor in your above post + the IH's, there was nice similar era IH near me here for 3K forget what model, was a TD, and it appeared to have a nice undercarriage. Your D2 is priced reasonably, if in good mechanical shape, winch is a nice feature too.