Intake is 0.006 (+ or - 0.001 inches)
Exhaust is 0.008 (+ or - 0.001 inches)
Checking the fuel flow is a good idea too. Hadn't thought if it either. Take a look to see if there's something inside the fuel tank blocking the filter inside it.
Thought I'd post these specs for Honda Engines.
Honda Small Engine Intake & Exhaust Valve Clearances
Model Series
Intake Valve Clearance
Exhaust Valve Clearance
GX640
0.10-0.14mm ( 0.004-0.006in )
0.18-0.22mm ( 0.007-0.009in )
GX100
0.15 +/- 0.04mm
0.20 +/- 0.04mm
GX120
0.15 +/- 0.02mm ( 0.006 +/- 0.001in )
0.20 +/- 0.02mm ( 0.008 +/- 0.001in )
GX160
0.15 +/- 0.02mm ( 0.006 +/- 0.001in )
0.20 +/- 0.02 mm ( 0.008 +/- 0.001 in )
GX670
0.15 +/- 0.02mm ( 0.006 +/- 0.001in )
0.20 +/- 0.02mm ( 0.008 +/- 0.001in )
GXV120
0.15 +/- 0.02mm ( 0.006 +/- 0.001in )
0.20 +/- 0.02mm ( 0.008 +/- 0.001in )
GXV140
0.13 - 0.17
0.18-0.22
GXV160
0.15 +/- 0.02mm ( 0.006 +/- 0.001in )
0.20 +/- 0.02mm ( 0.008 +/- 0.001in )
GXV270
0.15 +/- 0.02mm ( 0.006 +/- 0.001in )
0.20 +/- 0.02mm ( 0.008 +/- 0.001in
GX360
0.12 +/- 0.02mm ( 0.005 +/- 0.001in )
0.20 +/- 0.02mm ( 0.0078 +/- 0.0008in )