The manual says every 300 hrs. This one has 635 hrs. Manual says to remove rocker cover etc.... The rocker cover can't be removed without removing the extra bracing for the rear end on this machine .
Clean the area around plug and rocker cover before removing them .
In the lower pick I'm finding top dead center with a piece off copper tubing ( a piece of wooden dowel is best ) Keep it centered on the piston and rotate clutch till the intake valve ( the one on the carburetor side )stops in the closed position (up). This is the TDC on the compression/firing stroke .
Check gap with a feeler gauge (.004 to .006 ")
My intake valve was with in spec .
The exhaust was a little of . Use an Allan key to loosen set screw in center of adjusting nut .
Adjust and tighten set screw and recheck gap . Below is the fuse block under the hood . If for some reason the electric dump bed does not move check the 40 amp fuse (orange)it's probably corroded . I have a zip tie around them .