NGK 5531 gap .036
0.7 mm
.028 in.
.35
the gap is 0.012 to 0.016
0.5mm
0.024-0.028 inches 0.6-0.7 mm
.017........Is wrong !The ignition spark gap is .027
points gap 17
0.020 in.
Try 20 /1000 inch on this rototiller.
It has electronic ignition. No points to adjust. 1985 Honda XR100R does have points and a condenser, just bought one today, and the gap is between12 and 14 thousandths