Engine stops after releasing the gas pedal

Hi there,

we just finished a 318 engine build: 1977 318 block, 1964 crankshaft, heads and intake manifold. We decided to use the hydraulic cam, lifters and rocker arms of the 318.
I runs very fine and if you give it a little throttle it revs up easy. But if you take your foot of the pedal, it dies. With sudden start up it looks if there is no compression on several cylinders. If we let it rest for a while everything is fine...

What could be the problem?
Ideas are more than welcome!

Arend Huisman