[Shop-talk] It's A Simple Machine, Right?

[Brian Borgstede]

If it were an ordinary push mower, I would say flywheel key. Fairly common if you hit something and stop the engine suddenly. It might have a spark, but the timing would be off. Just a thought.

Sent from my iPhone

> On Jul 2, 2025, at 1:55 PM, Jeff Scarbrough <fishplate at gmail.com> wrote:
> 
> 
> I've got a puzzle...
> 
>  tl;dr - should I try the plug first, skip ahead and replace the coil, or is there something else I should try?
> 
> The patient is a Snapper rear-engine riding mower, a machine that's as simple as can be.  Powered by a B&S Intek 12.5 HP engine, another simple machine.
> 
> My friend was cutting his grass and managed to get the grass chute tangled up in some old fencing.  He got it loose, and continued to mow.  After a short distance, the mower quit running and would not restart.
> 
> I brought it into my shop and we started troubleshooting. I first tried ether - it seemed like it tried for a second, and then nothing.  Pulled the plug and it looked wet.  Turned the engine over with the plug connected and grounded, and observed a spark.  Not a magnificent spark, but a spark.  
> 
> Verified compression, but due to the position of the muffler, I could not get *any* of my compression testers to seal in the hole well.  But it pushed against my finger with some force.
> 
> Moved to the carb.  Pulled and inspected.  Float working, jet clear.
> 
> Put it all back together, and nothing.  
> 
> Pulled the ground wire off the magneto coil and no change.
> 
> So, I'm thinking weak coil.  Not completely dead, but not working under cylinder pressure.  Something else I read suggested a bad plug - this one was installed a month ago and has been working.  Date code on the engine indicates it was built on April Fools Day, 2008.
> 
> In the era of $15 lawn mower coils, I would throw one on with no qualms.  But at $40 or $50, I hesitate.
> 
> So,  tl;dr - should I try the plug first, skip ahead and replace the coil, or is there something else I should try?
> 
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