whitestormgaming

MFR Grinder.

Vanilla spawners take quite a while to "boot up" (10-45s if im not mistaken) for each spawn period, have a default range of 16 blocks for activation. So, dont expect them to be instantly there. And they will only spawn if conditions are met (witches need a light level of 7 or lower to spawn from the spawner)

If all the spawning conditions are met, they should start spawning very shortly.
How about you give us some screenshots to work with?
 
I can only guess, instead of giving you answers without a visual aid.