How have you attempted to test for spark? A new plug or at least a used one from a mower you know that works?
It's possible the stopper plugs in the G4 black plastic carby have jammed in the off position but not likely.
If the test determines no spark forthcoming, you are probably looking at having to take the engine covers off and the cooling fan at the top, to access the magneto and condenser underneath, which sit near the top crankshaft bearing in a round hollow under the fan.
The points may just need a clean or you may have to replace the magneto and/ or condenser.
