Timing

Hi all.
Just fitted new amc head.
Piston one at tdc.
Cam back in and sprocket and chain back on with Mark's aligned.
Turned engine manually by hand to check nothing collides( just being cautious)
Everything back together and connected.
Purge cycle 3 times.
Turns over on key but reluctant to fire.
Eventually fires but throttle response seems poor compared to before.
Is it possible to get timing out say 180 degrees and still run but poorly.
Thoughts please