i think it is too big gap
should be 0.8 to 1mm, as the HAL sensor is a "wire-coil) that change its own elctromagnteic field each time the magnet cross the field, so if the gap is too big, the elctro-mag field remains the same-> no signal to the IGI unit-> no spark!

can u please post some pics so we can get a better look on the matter?