Disconnect the single wire that connects at the front of the engine at the fan shroud. This is the "kill " wire. With the wire disconnected any normal way of preventing ignition is eliminited. When this connection is grounded all igniton is terminated. The grounding normally comes from either the kill switch up front or through the rev limiter. With this wire disconnected the ignition will always be "on". To shut off the engine you would have to pull the plug wires (both) or reduce the idle speed till it dies.
You can also check for spark by removing a spark plug then connecting the plug wire with the base of the plug is solidly grounded. Be sure the kill switch is in the run position and crank the engine while watching for spark across the plug gap.
No spark is caused by a bad diode wire, bad coil or bad plug wire.
If you have spark try a small amount of starting fluid spray into the carb intake, if it fires you have a fuel problem of some kind. If it doesn't fire look for an ignition problem.
Rev limiter cases often look a little "warped".
Hope this helps