The motor shut off switch on a Sting is paralleled to the reroll valve.
When the reroll valve takes too long to operate, the motor switch
pneumatic closes, through a large bleed provided between the two and
shuts off the motor.  There are two ways to fix the problem.  You can put
another bleed in the line and slow down the slaved switch pneumatic, or
you can make the reroll snappier (better).  That could be something
simple like sluggish linkage, poorly adjusted linkage, or something
loose in the linkage that slows things down.  Or it could be a leaking
or stiff (or both) reroll pneumatic.  It can also be the reroll
pneumatic mount, which is moving each time it goes into reroll, and
subtracting from the work done on the reroll linkage.  Good luck.

Craig B.