DuroStar DUROMAX DUAL FUEL XP8500EH User Manual page 59

4.
Measure plug gap
Measure the plug gap with a gauge. The gap should be 0.7-0.8
mm (0.028-0.031 in).
5.
Clean and re-gap
If you are re-using the spark plug, use a wire brush to clean
any dirt from around the spark plug base and then re-gap the
spark plug.
6.
Install spark plug
Screw the spark plug back into its place on the generator
using the spark plug wrench.
7.
Replace spark plug cap
Replace the spark plug cap.
59