Engine stops running after put in gear
 

I have a Plymouth with a 318 engine and a 904 automatic transmission.

The engine runs fine when it is in Park but a soon as I put it in drive the engine gives a "puff" and stops running.

Sometimes I manage to get the car rolling but as soon as I hit the gas pedal, again a puff and it stops running.

Any suggestions?

I'd start by checking the timing. It sounds like it might be retarded and doesn't have enough power to even hold idle with ANY load.