Garden tractor strange spark problem

[SleepyFarmall]

My garden tractor has a 8-HP Kohler engine, 1963 model I believe. Have had a problem for years where it would run good but then shut off after about an hour. Then recently, it would only run for a few minutes and shut down. Would not restart until you let it set for about another hour. Really frustrating. Well, yesterday I went to use it in my garden and it, of course, shut down and would not restart. Right then I tested the spark with this in-line spark tester (see picture) and it fired right up and ran all morning with the spark tester still installed. Strange, yes?
So, is the spark tester actually doing something to the spark or was this some kind of coincidence? If it is doing something to the spark that remedies the shut-down/no restart condition, what component do I need to replace to avoid having to use the spark tester? I'm weary of chasing my tail on this thing. Thank you, Michael

 

[Larry H.]

Spark Plug ?

 

[560Dennis]

easier for the ignition to fire across spark plug gap than in the original positron with wire tester installed . Put spark plug wire it back where you had it and see if it stalls .out. To verify the wire is shorting to ground. Might weak insulation shorting it out to frame some where.
If it stalls the old spark plug wire is breaking down arching out to frame .
check the coil for good ground .
if coil is very hot to touch its shorted out .
make sure the condenser is grounded.
clean points reset gap .
there’s a Kohler engine manual on line for more details about maintenance like k241 is 10 horsepower ,don’t remember what 8 hp are.

 

[Geo-TH,In]

I was chasing my tail with this coil

. You can't see what goes on inside a coil, especially a 1963 coil. High voltage causes insulation to break down in coils, distributor, rotor and spark plug wires. I had a spark plug go bad after running for a few minutes. It would work when cold, but stop when it got hot.
Go figure. Sometimes the only solution is to replace parts and chase your tail.

 

[Mike(NEOhio)]

Watch it in the dark to see if it's the plug wire as 560 suggested. I had a weed eater do that. Cut out after 10 minutes, cool down and run 5 minutes at a time. New coil, no change. It was the condenser. Adding the tester puts in another gap to jump. The coil will build to a higher voltage. I've had engines that misfired then with the wire off the plug and hanging two inches away the misfire disappeared. Could also be the coil, windings go open when it heats up.

 

[Mike(NEOhio)]

I was chasing my tail with this coilView attachment 114854. You can't see what goes on inside a coil, especially a 1963 coil. High voltage causes insulation to break down in coils, distributor, rotor and spark plug wires. I had a spark plug go bad after running for a few minutes. It would work when cold, but stop when it got hot.
Go figure. Sometimes the only solution is to replace parts and chase your tail.

This came in while I was typing. Coil can test OK cold. If you start throwing parts at it change the condenser first. A lot cheaper than a coil.

 

[Fritz Maurer]

Jumping the spark ahead of the plug makes it hotter, which is what is occurring with your tester; will sometimes overcome a fouled plug and run the engine. However, I have never seen a fouled plug cause an intermittent failure like you are describing... I think you have more than one issue at play here. I'd change the spark plug as a first step before dinking with rest of the ignition system.

 

[kencombs]

Jumping the spark ahead of the plug makes it hotter, which is what is occurring with your tester; will sometimes overcome a fouled plug and run the engine. However, I have never seen a fouled plug cause an intermittent failure like you are describing... I think you have more than one issue at play here. I'd change the spark plug as a first step before dinking with rest of the ignition system.

Yep, way back when it was common to see lots of lead and/or oil fouling on daily drivers. That conductive fouling causes the spark to leak off before it rises to a level high enough to jump the gap. So it never fires. Adding some resistance, like holding the wire off the plug a bit so it could jump would make them fire at idle. You could also put the wire boot on the plug, barely, so it would jump and 'solve' the miss for a while.

Try a new plug, even a resistor plug in a close heat range may help.

 

[BobTx]

First tractor I learned to drive was an oil-burning F-12 Farmall. Had to make a special fixture to hold the spark plug wires 1/4" off the spark plugs. Don't fully understand the principle but it would keep the 4 banger running all day long. BobTx

 

[Deere Mark]

Jumping the spark ahead of the plug makes it hotter, which is what is occurring with your tester; will sometimes overcome a fouled plug and run the engine. However, I have never seen a fouled plug cause an intermittent failure like you are describing... I think you have more than one issue at play here. I'd change the spark plug as a first step before dinking with rest of the ignition system.

Used to be able to buy this unit which has a spark gap inside. Place one end in the coil opening and plug the coil wire into the other end. Makes the engine (which has fouled plugs) run better.

 

[Brian G. NY]

Yep, way back when it was common to see lots of lead and/or oil fouling on daily drivers. That conductive fouling causes the spark to leak off before it rises to a level high enough to jump the gap. So it never fires. Adding some resistance, like holding the wire off the plug a bit so it could jump would make them fire at idle. You could also put the wire boot on the plug, barely, so it would jump and 'solve' the miss for a while.

Try a new plug, even a resistor plug in a close heat range may help.

We used to hold the wire just off the plug to get a snowmobile started when the plug was oil fouled......not uncommon back in the late 60s and early 70s when I was into that sorta thing.
Very few oil injected machines back then......the only one I knew of was a Yamaha a friend of mine had.