You can use up to 36-pound card stock via manual feed in the LaserWriter II
series printers. However, higher weight stock has a higher content of
cotton rag or other dust-producing material. This may be causing paper
dust to build up on the paper pickup roller and/or separation pad, which
may be causing the jam conditions.
Try cleaning the paper pickup roller with a printer platen cleaner. DO NOT
use alcohol. Alcohol removes an oil compound in the rubber, causing it to
shrink and damage the roller.
Note that the roller and separation pad are subject to wear. Ensure that
these parts are in good working condition.
Search on LaserWriter II and specifications for more information on recommended
printing material.