hello

I have a 2.0L 1972 (9/1972) porsche 914 and I have some problems with the gearbox.
My car is a europian model. Don't know if there is any diffrende between EU an USA.

When the engine turns I can't get the car in reverse or first gear.
When the engine isn't turning I can shift in first and reverse gear.

what could be the problem ?
And how can I adjust the gear shifter

you should check on the clutch adjustment first, because you can shift into first and reverse with the engine off it is unlikely that the shifter is in question.

The cable will stretch after time so it's probably time for an adjustment.

Reverse has no synchronizing parts so if you cant get into it that means it is still getting power from the engine (clutch not disengaging). Clutch should start to slip at 1/4-1/3 pedal travel.