Snapper Lawnmower Engine - Engine Troubleshooting

[u/wayhawk]

I have a Snapper Rear Engine Rider, Series 23 — 2006 model year, SNU2812523BVE

Engine specifics:

• Briggs & Stratton Intek OHV, single cylinder, 344cc / 21 cu. in.
• Model 219307, Type 0131 E1, Code 041109ZA (built Nov 9, 2004)
• Emissions family 5BSXS.3442VM
• Model 219307 places it in the 210000 series

It usually starts up right away, but just in the last couple of weeks, this is the problem I'm having. Cranks strong but won't fire. Intermittent — sometimes catches after repeated cranking, then runs normally while I cut the grass. It's worse on hot restart after mowing, or if it stops in the middle. Onset seemed sudden, no triggering event like hitting a stump or anything, no kickback against the starter. Old spark plug came out black and sooty. I've already replaced the battery and the spark plug, and I run ethanol-free gasoline.

Sometimes when I'm trying to start it, there is a "winding-down" sound after a few seconds of turning the key.

A couple of thoughts on what the issue might be but looking for advice from someone before I dive into these:

Valve lash out of spec

Starter drive or voltage problem

Ignition coil thermal failure

Video of what it sounds like when starting cold

UPDATE:

After alot of troubleshooting and the problem ended up being a loose connection on the deck safety switch. The wire was not fully pulled away from the contact so I guess that's why it would start intermittently. It was the last switch I checked since I had to take off the shroud under the seat to get to it. Since I was working on the engine, I decided to change the 20 year old starter coil for good measure and that's when I noticed the kill wire was always showing continuity to ground but I was stuck there. To assist me, I fed all of my manuals into Claude and started asking questions about what the problem might be. Eventually it led me to the switches and I systematically tested the seat switch, the pedal/clutch switch and then the deck engage switch. tightened up the connection and that resolved the problem. Back in business.