Robbins 350 ignition coil problem

I have a 350 Robbins (MCI with Pre-MCI coil & ignitor) that will only produce one "spark" on both plugs each time the accelerator is pressed & held in the run position,if I come off of the accelerator & press it again it only sparks once :?.The coil is from a known good running engine;any input is welcomed as to what the culprit may be.