A Harley Davidson twin cam Fat Boy should be set with a gap of .40 inches. This is equal to 10 mm.
The suggested spark plug gap for a 1973 Harley Davidson is 0.040. It is the suggested gap for most of the spark plugs of that era.
.040"
40
The spark plug gap should be .040"
the gap for a Harley plug on a 88c.i. is 30
35
.040
1.00 mm
.040".
.040
Trouble code P0305 means:Cylinder 5 misfire detected Try replacing the plug wires and double checking the spark plug gaps
40