Many of Gottlieb's EM machines suffered from under-powered flippers. Part
of this is due to them being engineered weaker than those of other
manufacturers. One way to strengthen those Gottlieb flippers is to replace
the A-5141 flipper coil with a modified A-5141 which is available from
several popular suppliers.
By the way, I intentionally do not mention specific suppliers in these tips
so as to maintain my objectivity and independence.