Let's try to work through this a step at a time. First, to test the spark, take an old spark plug that has been used in a 4 stroke engine (2 strokes ruin spark plugs; in general 4 strokes don't, or at least not quickly), open the gap to 3 mm, connect it to the spark plug lead, clamp the spark plug body to the cylinder head so it makes contact, remove the "real" spark plug from the plug hole, put the controls in the starting position (so the spark won't be disabled), pull the start cord, and watch the enlarged spark plug gap. Expect to see a blue spark every second revolution of the engine. If the spark is red or orange, or irregular, you have ignition trouble. A consistent blue spark means ignition intensity is not the source of your starting problem.
The next thing to check is the valve clearance: 0.1 mm intake, 0.15 mm exhaust.
If you have access to a compression pressure gauge, it should read about 10 kg/square cm, or 140 psi, pulling it over briskly with the throttle open (600 rpm). It would take several pulls to show maximum pressure. If the compression feels normal this test is not essential, but is nevertheless useful.
If it passes all the tests so far, you should check whether the problem is fuel feed. The simple, crude way to test this is to remove the air cleaner and squirt a few cc of fuel into the carburetor air intake (or at a pinch, into the cylinder through the spark plug hole) then use the standard Honda starting procedure. Stand clear of the carburetor air intake, in case it spits burning fuel. If it starts when primed in this way, the starting problem is getting fuel into and through the carburetor jet; we can talk about what might be wrong if that turns out to be the problem.
