Need help with Murray lawnmower - won't start

Factual Questions
1

The battery is new and good and the starter turns the engine.

The other day, when I poured a little gas into the intake, it backfired. Now I can’t even get it to do that. I disconnected the spark plug wire and stuck a screwdriver into the lead and looked for a spark and I’m getting nothing.

Is it possible that the magneto is bad or weak? I tried gapping the magneto with a thin piece of cardstock and that didn’t help.

I’ve checked the safety switch under the seat and it’s working properly (it grounds out when you take weight off the seat which kills the engine).

I don’t think it would be a safety interlock with the transmission because the starter wouldn’t turn.

What else do I need to look for?

2

Disconnecting the spark plug lead and sticking a screwdriver in it doesn’t make sense. Remove the spark plug, connect it to the lead, hold the bottom electrode against the block, have someone else sit in the seat, and crank the engine. Does it spark? If so, you have a fuel problem, (assuming the connecting rod, piston, and valves are present and doing what they should do).

Beyond that, you’ll need an interlock safety circuit diagram to troubleshoot further.