What was wrong with this mower?

[scoyote]

Yes it's true--the plug can show you it can spark but under load it can fail

 

[slomo]

so you had fuel, spark, and compression. that only leaves spark at the correct time?

Little air works too.

 

[slomo]

I try to preach about electrical circuits on here. All need load tested. I would of caught it with the ol' PET-4000. Easy as pie......

 

[Scrubcadet10]

Little air works too.

That's fuel.

 

[jdtm]

I try to preach about electrical circuits on here. All need load tested. I would of caught it with the ol' PET-4000. Easy as pie......

For everyone's reference, here is the PET-4000 in action:

I am curious. Would you describe how it would have caught this problem?

 

[slomo]

For everyone's reference, here is the PET-4000 in action:

I am curious. Would you describe how it would have caught this problem?

The further you wind out the ground pin the more stress it creates on the coil to produce spark. You wind it out slow till it dies. Take note of the knob position.

Grounding a plug to the metal shroud puts a small load on the coil. The PET can tell you a lot more. It will fully stress the coil.

 

[slomo]

That's fuel.

You left out air in post 16, way back. Air, fuel, spark and compression. Just like Betty Crocker.

 

[bertsmobile1]

The further you wind out the ground pin the more stress it creates on the coil to produce spark. You wind it out slow till it dies. Take note of the knob position.

Grounding a plug to the metal shroud puts a small load on the coil. The PET can tell you a lot more. It will fully stress the coil.

Actually that is totally wrong
You can not add stress in any way shape or form to a magneto coil
Widening the gap just adds resistance to the circuit
The higher the resistance the greater the VOLTAGE required to jump the gap
So it is a round about way of checking the out put voltage of the coil.
The down side of using one is electricity will follow the path of least resistance so if the insulation on a functioning coil is getting thin then then the coil may develope an internal short rather than jumping the gap so winding it out till the spark is estinguished is very bad for the coil.
Once it has done that then a tracking path is established and the coil will continue to short down that path .
Once a voltage has been induced in a coil, it HAS to go some where so if your super tool prevents it discharging down the spark plug wire , it still has to discharge some where and that will be internally, to the detriment of the magneto coil .
BAck in the 20's , 30's & 40's then again in the 90's snake oil salesmen sold a high resistance kit called "Spark intensifers " and the latter versions were called Power spark or some trash like that with all of the usual BS about more power, better milage etc etc etc .
The simple 3 point spark tester / magneto tested has been around for over 100 years and are usually made specifically for a particular engine with the large gap set at a safe separation to prevent internal tracking
Because extra voltage is required to jump the gap the induced voltage is retained in the coil winding for longer so they get hotter which in cars & motorcycle with discreet magnetos ( ie not flywheel ones ) can lead to premature failure of the magneto .
All of the snake oil jobs did just that so after a while owners started to sue the makers & eventually they got banned every where on the planet except the USA

 

[Scrubcadet10]

Actually that is totally wrong
You can not add stress in any way shape or form to a magneto coil
Widening the gap just adds resistance to the circuit
The higher the resistance the greater the VOLTAGE required to jump the gap
So it is a round about way of checking the out put voltage of the coil.
The down side of using one is electricity will follow the path of least resistance so if the insulation on a functioning coil is getting thin then then the coil may develope an internal short rather than jumping the gap so winding it out till the spark is estinguished is very bad for the coil.
Once it has done that then a tracking path is established and the coil will continue to short down that path .
Once a voltage has been induced in a coil, it HAS to go some where so if your super tool prevents it discharging down the spark plug wire , it still has to discharge some where and that will be internally, to the detriment of the magneto coil .
BAck in the 20's , 30's & 40's then again in the 90's snake oil salesmen sold a high resistance kit called "Spark intensifers " and the latter versions were called Power spark or some trash like that with all of the usual BS about more power, better milage etc etc etc .
The simple 3 point spark tester / magneto tested has been around for over 100 years and are usually made specifically for a particular engine with the large gap set at a safe separation to prevent internal tracking
Because extra voltage is required to jump the gap the induced voltage is retained in the coil winding for longer so they get hotter which in cars & motorcycle with discreet magnetos ( ie not flywheel ones ) can lead to premature failure of the magneto .
All of the snake oil jobs did just that so after a while owners started to sue the makers & eventually they got banned every where on the planet except the USA

I just test them with my briggs tester, it's got about a 1/4" gap to jump.

 

[jdtm]

Actually that is totally wrong
You can not add stress in any way shape or form to a magneto coil
Widening the gap just adds resistance to the circuit
The higher the resistance the greater the VOLTAGE required to jump the gap

I think "standoff voltage" would be more accurate than stress. From an electrical perspective the idea is that the insulation will be more likely to fail due to the need to withstand greater voltage. From your later comments, you seem to agree.

Widening the gap increases the breakdown voltage. Once the spark is started, the voltage drops to nearly 0 even if the gap is made much wider.

Once a voltage has been induced in a coil, it HAS to go some where so if your super tool prevents it discharging down the spark plug wire , it still has to discharge some where and that will be internally, to the detriment of the magneto coil .

Current has to go somewhere since it is a flow of charged particles, but that is different from voltage. Voltage does not have to go anywhere. It seems perfectly content not jumping out at an unsuspecting person looking at a wall outlet. However, forcing equipment to operate at higher voltages than it was designed to tolerate, such as using a coil/magneto with a wider spark gap will increase the demands on its insulation, which can cause the failure you described.