As you are not too specific about which 4 litre engine you are referring, a good rule of thumb is 0.05 inches.
the spark plug gap is .40
The correct spark plug gap is 40 thousands on a stock harley plug
.40 gap
spark plug gap is 1.04 mm or .40 inch
what is the spark plug jd 175 hydro
.40
.40
40
.35 to .40
.38 to .40
35 to 40 percent gap
.40 gap