a904 and carb help!

Too easy !
it could simply be that the KD band needs adjustment.
If reverse works then the L/R band is fine, and the Hi-drum is fine.
If the car moves forward, then the Forward clutch is working.
So the only thing Not working is the KD band.
In all likelyhood, the band just needs adjusting, but if not, then perhaps, the band broke or the strut fell out, or I suppose the servo exploded lol, or the 1-2 valve is stuck.
Easy fix for all except the band replacement, but if a band adjustment doesn't do it, then, the pan/ VB have got to come down for a visual.