Carb tuning, larger accelerator pump nozzle?
When the clutch lets out, the load on the engine increases and the engine slows slightly. Any slowing results in lower vacuum. Lower vacuum means less pressure differential so as the clutch lets out it will be a little leaner than the setting in neutral. Its easier to see this on a automatic.
This going the other way, drive into park (neutral).
Are you sure it doesn't drop below 20 degrees at when the rpms drop to 750?
I've not worked with that distributor but most have some method of adjusting the preload on the springs.
A typical Chrysler distributor, even a mopar performance one, will come setup so it start advancing around 750 rpm.
When the clutch lets out, the load on the engine increases and the engine slows slightly. Any slowing results in lower vacuum. Lower vacuum means less pressure differential so as the clutch lets out it will be a little leaner than the setting in neutral. Its easier to see this on a automatic.
This going the other way, drive into park (neutral).
This could be messing with you.
Are you sure it doesn't drop below 20 degrees at when the rpms drop to 750?
I've not worked with that distributor but most have some method of adjusting the preload on the springs.
A typical Chrysler distributor, even a mopar performance one, will come setup so it start advancing around 750 rpm.