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I recently came to visit my daughter and she said her lawn mower will not run first I replaced the spark plug still no spark then I pulled the pull rope cover off and inspected the coil found that it was Rusty apparently been leaving it outside so I've replaced the coil clean the flywheel and still no spark any help would be appreciated

Did you set the gap on the coil / magneto ? Not sure what the setting is but probably .010-.020 or thereabouts to start and see if it generates a spark,

Drain gas from tank, fill with fresh gas. Recheck spark plug gap at .030. Did you gap coil to flywheel at .010 with business card? Remove & inspect flywheel key at crankshaft. Clean underside of mower. Adjust valves to specs with engine cold. Check oil level on dipstick & smell for gas in oil. Please report back with engine make, model, & serial #'s, thanks Mark

Bertrrr said:

Did you set the gap on the coil / magneto ? Not sure what the setting is but probably .010-.020 or thereabouts to start and see if it generates a spark,

Click to expand...

I set the air cap at 14 and unplug the kill wire in case it was rubbed through somewhere I am completely baffled magnet on a flywheel and a coil and it should make spark but it doesn't

If you are old enough you will remember points & capacitors which were an eternal problem on mowers
Well in 1962 quality mowers replaced the points with a Hall Effect Trigger
American mower companies were too cheap / stubborn / nationalistic to replace the points till around 1990 when the Australian patient ran out .
For the next few years they used an external trigger unit then some smart arse worked out they could embed the chip into the coil and change the coil from a $ 5 part to a $ 50 part which was a good money maker as the chip cost 25¢
So if you remove the kill wire & you get no spark then either the cap on the spark plug lead has gone bad or the chip has gone bad

PS rust on the flywheel & / or ignition module ( previously called a coil ) have zero effect unless it is thick enough to touch together as the magnet passes the magneto legs
Having said that corrosion between the mounting plate & the ignition module can cause a bad ground but is the 12 years I have been doing this for a living I am yet to find this to be a problem unless the engine was stored without the magneto module in place .

So if you have no spark with the kill wire off , time for a new module

bertsmobile1 said:

If you are old enough you will remember points & capacitors which were an eternal problem on mowers
Well in 1962 quality mowers replaced the points with a Hall Effect Trigger
American mower companies were too cheap / stubborn / nationalistic to replace the points till around 1990 when the Australian patient ran out .
For the next few years they used an external trigger unit then some smart arse worked out they could embed the chip into the coil and change the coil from a $ 5 part to a $ 50 part which was a good money maker as the chip cost 25¢
So if you remove the kill wire & you get no spark then either the cap on the spark plug lead has gone bad or the chip has gone bad

PS rust on the flywheel & / or ignition module ( previously called a coil ) have zero effect unless it is thick enough to touch together as the magnet passes the magneto legs
Having said that corrosion between the mounting plate & the ignition module can cause a bad ground but is the 12 years I have been doing this for a living I am yet to find this to be a problem unless the engine was stored without the magneto module in place .

So if you have no spark with the kill wire off , time for a new module

Click to expand...

So you said you have replaced the coil and still no spark. Did you order a new coil based on the engine model number? Do the new and old coil look pretty much the same? Have you tried checking for spark with and without kill wire? Have you tried a different spark plug?

New plug

Tiger Small Engine said:

So you said you have replaced the coil and still no spark. Did you order a new coil based on the engine model number? Do the new and old coil look pretty much the same? Have you tried checking for spark with and without kill wire? Have you tried a different spark plug?

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I purchased a new plug still no spark I called the local small engine shop gave them the model number of the engine they had a new coil I took the old coil and compared them identical still no spark

captain oblivious said:

New plug

I purchased a new plug still no spark I called the local small engine shop gave them the model number of the engine they had a new coil I took the old coil and compared them identical still no spark

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That mower is haunted. I suggest you take to your local priest and have a priest perform a exorcism on it.

How are you checking for spark?

PTmowerMech said:

That mower is haunted. I suggest you take to your local priest and have a priest perform a exorcism on it.

How are you checking for spark?

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The last time I literally stuck a screwdriver into the plug wire and held on to it didn't get the least amount of shock I've never seen a bad flywheel but that's where I'm at it's still magnetic I have no clue why this thing is not getting spark and yes it very well could be cursed

Try that again while touching off on ground with your hand , if it is a good spark it should make your muscles react

Bertrrr said:

Try that again while touching off on ground with your hand , if it is a good spark it should make your muscles react

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I was thinking about that ground thing too. Hard to pull the pull chord, while grounding the coil at the same time. One almost has to have two people. Unless you have one of these.

captain oblivious said:

The last time I literally stuck a screwdriver into the plug wire and held on to it didn't get the least amount of shock I've never seen a bad flywheel but that's where I'm at it's still magnetic I have no clue why this thing is not getting spark and yes it very well could be cursed

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Just for grins, pour a little gas or some carb cleaner into the plug hole or through the carb and give it a pull and see if it tries to start.

Also note that the magneto "module" is polarity sensitive
If you put it on upside down it will not work ( unless it was a factory reject )
Well it will work but the spark will be very weak & way out of time
Most go on with the kill wire down which looks wrong because the HT lead seems to going the wrong way
Some have "This Side UP ' or "cylinder side " or "Engine Side" cast into them.
There was a batch on Evilpay down here a few years ago where the writing was on the wrong side
There was also a batch that were wired wrong and would only work if installed upside down that did not have the writing on them .
Simple test for the magnet strength is to fit the coil as far away as the slot will allow then bring the magnet around and loosen the screws
A good magnet will cause the magneto to snap onto it quite strongly

Pull the spark plug and you can easily pull the cord and watch for reaction

A bad spark plug wire sounds like the issue. You might have gotten a new coil that is defective too...

Corrosion where coil mounts ? It has to have good contact to work.

There are simple testing devices for the ignition available. I myself bought this one. Check in a dark room, during daylight the light is not really visible. Then You will be sure it is an ignition problem. If you have no spark, it is a gasoline supply problem. Another way is to spray start spray into the air filter. If the engine starts for a few seconds and halts again, you are sure, it is a gasoline problem. if it does not run at all, it may be either problem.

I just blew thru the posts - all good stuff. But I didn't see anything about a new spark plug. Start with the easy stuff first. Get a new plug that matches the specs of the engine. Gap it properly and try it again. Maybe a good cleaning of the plug boot and a little dielectric grease.

Law57 said:

I just blew thru the posts - all good stuff. But I didn't see anything about a new spark plug. Start with the easy stuff first. Get a new plug that matches the specs of the engine. Gap it properly and try it again. Maybe a good cleaning of the plug boot and a little dielectric grease.

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Yes plugs do fail weirdly at times. Even new plugs can be faulty which is why I suggest using a known good for testing.

You really don't know if you have a spark or not. Often plugs are firing but depending on lighting conditions we can't see it.

Buy yourself a $5 adjustable gap spark tester on amazon or ebay. They allow for a very wide gap and high voltage used on cars, but you use it in the close lawn mower range. Really any visible spark there, and it's time to move to something else as the problem!

I suspect that your mower is permanently grounded by corrosion closing the circuit at the kill switch. Pull the bale as if you were going to start the mower. Tie a string around it and the handle to keep it up. Now trace the cable housing down to the side of the engine and make sure there is an air gap. You may need to clean it or even bend the tab a little to ensure you are not grounding out the coil.

This reminds me of how we used to check a 9v battery by putting it to our tongues. How do you check for 120\240 volts a-c?

captain oblivious said:

I recently came to visit my daughter and she said her lawn mower will not run first I replaced the spark plug still no spark then I pulled the pull rope cover off and inspected the coil found that it was Rusty apparently been leaving it outside so I've replaced the coil clean the flywheel and still no spark any help would be appreciated

Click to expand...

Is it possible you have a new 'bad' coil? I keep the following as a reference
Coils and resistance measures
B - base
K - kill
S - spark

B - K 2k - 18k
B - S 2k - 18k
K - S 10k - 30k

Mower coil
Red probe to Spark boot
Black probe to base ground
Should show 2.5 to 5K
If infinity, then the coil is open and no good

Make sure coil is not installed upside down.

bertsmobile1 said:

Also note that the magneto "module" is polarity sensitive
If you put it on upside down it will not work ( unless it was a factory reject )
Well it will work but the spark will be very weak & way out of time
Most go on with the kill wire down which looks wrong because the HT lead seems to going the wrong way
Some have "This Side UP ' or "cylinder side " or "Engine Side" cast into them.
There was a batch on Evilpay down here a few years ago where the writing was on the wrong side
There was also a batch that were wired wrong and would only work if installed upside down that did not have the writing on them .
Simple test for the magnet strength is to fit the coil as far away as the slot will allow then bring the magnet around and loosen the screws
A good magnet will cause the magneto to snap onto it quite strongly

Click to expand...

johnny7 said:

Is it possible you have a new 'bad' coil? I keep the following as a reference
Coils and resistance measures
B - base
K - kill
S - spark

B - K 2k - 18k
B - S 2k - 18k
K - S 10k - 30k

Mower coil
Red probe to Spark boot
Black probe to base ground
Should show 2.5 to 5K
If infinity, then the coil is open and no good

Click to expand...

Havent been on the forum in long time and thankful for this thread and all the LB experts lending hand to this issue, I HAVE THE IDENTICAL ISSUE with my 1980s LB and this thread should help me maybe resolve. I'm pretty handy but know nothing about electrical
Likewise put a new ????? ( magnetic thing on flywheel, im old here and blanking on name )on it and still no spark. I suspect it relates to kill switch, who i bought it from installed makeshift kill switch to the housing with a toggle switch and a wire or two disconnected. If i come back with a pic of that i bet one of you guys can tell me what to do with it, suspect that could be my problem with a simple fix. This is a great thread, thanks from me as well for all this input from all.

I assume that this is a newer lawnmower the type that you have to hold the handle down in order to start it. At the point where the handle meets the connection on the mower pull that lever back with your finger. The zone control cable may not be working properly and not fully releasing the cutoff switch. That would cause the problem that you are facing.

Look for a dirt dauber wasp nest anywhere on the electrical system. They take no prisoners.

How old is the mower, does it have any safety devices such as a handle that has to be held against the pushbar , or a kill button ? I've seen brand new fresh out of thw box coils that were no good,and it only requires a multi meter to test a coil to see if it is within specs.. Remove a known working spark plug from anything that runs properly and stick it into the spark plug boot,ground the spark plug tip against a head bolt while spinning engine over. If no spark then you've eliminated the spark plug as the problem. Borrow a coil off of a know running like brand engine and swap it out to ascertain if it is the coil or not,test the spark plug wire for resistance using a multimeter to see if its bad or not..

To confirm whether the coil is producing a spark, disconnect the small wire that is connected to a tab on the coil and retest. This will disable any of the safety switches that may be keeping the coil from generating a spark. If you now have spark, correct the safety switch problem. NOTE: If the engine starts, you will have to reconnect the wire to the coil to stop the engine.

If there is still no spark, recheck the air gap using a business card or feeler gauge and also confirm the orientation of the coil mounting as another reply already stated. I recently replaced a failed coil on an older machine with a non-OEM coil and had to mount it upside down from what would have been the normal direction for the plug wires to exit in order for it to generate a spark.

I

captain oblivious said:

I recently came to visit my daughter and she said her lawn mower will not run first I replaced the spark plug still no spark then I pulled the pull rope cover off and inspected the coil found that it was Rusty apparently been leaving it outside so I've replaced the coil clean the flywheel and still no spark any help would be appreciated

Click to expand...

Did you actually ground the spark plug to the mower when you checked for spark? It won't spark if held in the air. I looked thru all of the responses and it wasn't mentioned unless maybe I missed it.

You probably sheared the flywheel key! Remove the starting cover to show the flywheel. Remove the centre nut. If it has a starting cup, remove it and put the nut on so it’s at the top of the crankshaft. Turn the magnet so that it’s on the back right hand side of the engine (by where the cover bolt goes-that area. Take a prybar and put under the flywheel where the magnet would be. Gently take a hammer and hit the top of the nut on the crankshaft while pressing down on the prybar. This should pop the flywheel. Remove the nut and the flywheel and there is a flywheel key. I’m sure you will find that it’s sheared. When you get a new one, put the flywheel on, and you will see the space for the key. Put it in, then the starting cup, washer and nut. To tighten so you don’t shear it again. Hold the blade with one hand and tighten the nut down with the socket and ratchet with the other hand. Put the rest back together. You could also probably take the new coil back and put the old one back on. Note: while working on the machine, remove the spark plug for your safety.

The Specialist said:

You probably sheared the flywheel key! Remove the starting cover to show the flywheel. Remove the centre nut. If it has a starting cup, remove it and put the nut on so it’s at the top of the crankshaft. Turn the magnet so that it’s on the back right hand side of the engine (by where the cover bolt goes-that area. Take a prybar and put under the flywheel where the magnet would be. Gently take a hammer and hit the top of the nut on the crankshaft while pressing down on the prybar. This should pop the flywheel. Remove the nut and the flywheel and there is a flywheel key. I’m sure you will find that it’s sheared. When you get a new one, put the flywheel on, and you will see the space for the key. Put it in, then the starting cup, washer and nut. To tighten so you don’t shear it again. Hold the blade with one hand and tighten the nut down with the socket and ratchet with the other hand. Put the rest back together. You could also probably take the new coil back and put the old one back on. Note: while working on the machine, remove the spark plug for your safety.

Click to expand...

Boy haven't you ever heard of using a torque wrench. Under torquing will allow flywheel to shear the key again while over torquing can damage the flywheel.

Here is an image where someone over torqued with an impact and then try to repair it.

Have you checked the shear pin in the flywheel? If it is even partially sheared you will get no spark.

captain oblivious said:

I recently came to visit my daughter and she said her lawn mower will not run first I replaced the spark plug still no spark then I pulled the pull rope cover off and inspected the coil found that it was Rusty apparently been leaving it outside so I've replaced the coil clean the flywheel and still no spark any help would be appreciated

Click to expand...

Try the old spark plug again.

StarTech said:

Boy haven't you ever heard of using a torque wrench. Under torquing will allow flywheel to shear the key again while over torquing can damage the flywheel.

Here is an image where someone over torqued with an impact and then try to repair it.

Click to expand...

Since that flywheel is spinning at 3600 RPM, that repair job would put the flywheel way out of balance and would vibrate the mower like crazy. Whoever repaired that gets the Darwin award for a mower repair.

Zedo said:

Since that flywheel is spinning at 3600 RPM, that repair job would put the flywheel way out of balance and would vibrate the mower like crazy. Whoever repaired that gets the Darwin award for a mower repair.

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Obviously you are not a technician! Most people on here don’t have torque wrenches etc. you can’t put a flywheel out of balance unless you take pieces out of it! I’ve done small engine repair for 38 years, so don’t try an BS me!

Zedo said:

Since that flywheel is spinning at 3600 RPM, that repair job would put the flywheel way out of balance and would vibrate the mower like crazy. Whoever repaired that gets the Darwin award for a mower repair.

Click to expand...

A lot of people don’t have torque wrenches. That’s why I stated to hang onto the blade and tighten the nut with a socket and ratchet. He never stated anything about impact guns etc. I’ve done this for 38 years. What are your qualifications? Last count, I have 25 manufactures certification and a large number of awards!

The Specialist said:

A lot of people don’t have torque wrenches. That’s why I stated to hang onto the blade and tighten the nut with a socket and ratchet. He never stated anything about impact guns etc. I’ve done this for 38 years. What are your qualifications? Last count, I have 25 manufactures certification and a large number of awards!

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Then you should know flywheel nuts should be torqued to manufacturers specs. I have 3 push mowers and I torque them at around 55 foot pounds. Sure the 'hold the blade and tighten the nut' will work , and I am an ASE certified auto mechanic for 35 years and every bolt on a vehicle has a torque setting. Just sayin'. I never mentioned anything about an impact gun.

The Specialist said:

Obviously you are not a technician! Most people on here don’t have torque wrenches etc. you can’t put a flywheel out of balance unless you take pieces out of it! I’ve done small engine repair for 38 years, so don’t try an BS me!

Click to expand...

Not wanting to argue but any handy person should own a torque wrench. They are cheap as dirt and you're asking for trouble if you don't use one. https://www.harborfreight.com/hand-...e-10-150-ft-lb-click-torque-wrench-63882.html.

Check the engine brake cable if the cable doesn't pull far enough, you'll never get a spark.

StarTech said:

Boy haven't you ever heard of using a torque wrench. Under torquing will allow flywheel to shear the key again while over torquing can damage the flywheel.

Here is an image where someone over torqued with an impact and then try to repair it.

Click to expand...

Thanks for the photo!
thats crazy bro!

The OP hasn’t posted since Monday I think he is FO!

captain oblivious said:

I recently came to visit my daughter and she said her lawn mower will not run first I replaced the spark plug still no spark then I pulled the pull rope cover off and inspected the coil found that it was Rusty apparently been leaving it outside so I've replaced the coil clean the flywheel and still no spark any help would be appreciated

Click to expand...

That happened to my uncle. It was the “Key” that breaks off to protect the motor should your daughter hit a rock. If I remember correctly it was on the shaft to the flywheel. I do remember it was a really easy, quick and cheap fix. It’s a tiny sacrificial piece of soft metal found at any hardware store.

mgmine said:

I assume that this is a newer lawnmower the type that you have to hold the handle down in order to start it. At the point where the handle meets the connection on the mower pull that lever back with your finger. The zone control cable may not be working properly and not fully releasing the cutoff switch. That would cause the problem that you are facing.

Click to expand...

My mower has that same trouble. The linkage under the shroud gets sticky, and I have intermittent stalls. What a pain, but a little sleuthing found the issue.

The troubleshooting procedure is being done properly so something is being overlooked.
When you don't have spark jumping the Gap at a plug, the first basic easy test is to throw a known good plug in there preferably an older dirtier one because it's easier to see the spark if you still don't have spark it's either the kill switch wire is grounded or the module is bad.
So then you have to pull the shroud off and take the small kill switch wire off of the coil and retest.
Now this means the child has to go back on because spending it by hand is not going to cut it.

If you still have no spark and you haven't taken anything else apart and you know the mower ran before, then there is a 99.999999 and however much more you want to go likelihood that you have a bad coil / ignition module / magneto whatever you want to call that too.

Something is being overlooked or if the magneto has been swapped, it's not the right one etc

captain oblivious said:

I recently came to visit my daughter and she said her lawn mower will not run first I replaced the spark plug still no spark then I pulled the pull rope cover off and inspected the coil found that it was Rusty apparently been leaving it outside so I've replaced the coil clean the flywheel and still no spark any help would be appreciated

Click to expand...

All good recommendations but didn’t see a comment about the safety cut out switch feature. This switch is designed to prevent a spark if not assembled properly or maybe you have a faulty switch. When I reassembled my 5.5Hp Snapper mower I hand the same problem, no spark. I remembered a mower tech warn me about this feature and sure enough the blower housing tube was not contacting the safety cutout switch during re-installation because the plastic mounting flange had cracked. I re-aligned it and it started right up. See attached photos.
Hope this helps.

lowmow said:

Have you checked the shear pin in the flywheel? If it is even partially sheared you will get no spark.

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You will have spark, just not at the correct time

Did you install the coil upside down?

sessman55 said:

Did you install the coil upside down?

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We see that all the time people put them on upside down and bring them back that is the first thing we ask them. They are marked cylinder side or this side up. Hard to see but is there.

captain oblivious said:

I recently came to visit my daughter and she said her lawn mower will not run first I replaced the spark plug still no spark then I pulled the pull rope cover off and inspected the coil found that it was Rusty apparently been leaving it outside so I've replaced the coil clean the flywheel and still no spark any help would be appreciated

Click to expand...

Buy one if these & test for spark in dim light. That way you know for certain that it is or isn’t a spark problem.

texasvet said:

Buy one if these & test for spark in dim light. That way you know for certain that it is or isn’t a spark problem.

Amazon.com

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Maybe OP did use a spark tester. I always use mine to check for spark before buying a new coil, but I also check to see if the coil is being inadvertently grounded. If the kill switch is not being opened when you pull back the bale, the spark will be grounded and your tester will show a no spark condition. The OP said that the mower was rusty from sitting outside under a tarp. I Not much to go on but is consistent with a rusted/corroded kill switch that is grounding out the spark. You can pull the ground wire off the coil and if that gets you spark, then you know you have a good coil but bad kill switch or other inadvertent ground. Another option if you suspect the kill switch is to insert a nonconductive material between the two connectors on the kill switch and see if the mower starts. I use a 3 inch by 1/2 inch strip of plastic I cut from a milk jug so when the engine starts I can easily pull the plastic strip out and shut down the engine, which is easier than fooling with the connection on the coil. If OP has tested and excluded bad ground then I’d suggest he ask daughter if she ran over a stump or rock just before motor stopped. If so, pull the flywheel off and check for sheared key. That would result in defective ignition timing, ie: he’d have spark, but not when he needed it, so again not a condition where a spark tester tells the whole story.

anejohn said:

All good recommendations but didn’t see a comment about the safety cut out switch feature. This switch is designed to prevent a spark if not assembled properly or maybe you have a faulty switch. When I reassembled my 5.5Hp Snapper mower I hand the same problem, no spark. I remembered a mower tech warn me about this feature and sure enough the blower housing tube was not contacting the safety cutout switch during re-installation because the plastic mounting flange had cracked. I re-aligned it and it started right up. See attached photos.
Hope this helps.

Click to expand...

Highly unlikely in the OP's case because most likely they are talking about one of the much more common vision statin lawn mowers of the past 25 or so years which don't have that feature anyways..
The engine you pictured is of the mid 80s probably at newest with quite a few different designs in it. Lol
The thing about basically all the safety switches on mowers, and even vacuums and blowers and things that have extra safeties for shoots, discharges etc is once you take the shroud off and get to the actual coil, all you have to do is remove the small kill switch wire on the coil and then none of the other safeties matter at all because it disables everything and the the vast majority of all small outdoor power engines like this use whatever kill switches they may have to go right back to this wire to do the same end result.
So you pull one wire, you eliminate them all for test purposes.

It is common to have one of your other safeties causing a no start or even no crank condition on some of the smaller riders because they add extra ones like this.
I've had the leaf vac chippers come in multiple times with the rear discharge button not being pushed down because the plastic / metal tab that presses on it tweaks over the years and doesn't push down enough.
I'm also seen another style with one over on the side that was messed up and I've seen plenty of the rear engine riders mostly of the MTD manufacturer and the Craftsman r1000 which is also made by them where the discharge shoot or mulch cover isn't pressing on that plunger safety switch because it's bumped into something so the machine won't crank.
Then you have the low oil shutdowns on generators which can also create a problem.
But with all these situations if you're testing, when you get to the actual coil and remove the wire, it has no choice but to spark when you spit it if the ignition module is working because you have eliminated all forms of kill switch which would be grounding out the coil which is all it does anyways as far as spark goes. On the rear engine riders I mentioned it's actually part of the electrical system and not the kill switch system because it prevents it from cranking just like parking brake switch and the blade engagement switch would do so it really has nothing to do with spark and on most all of these, if you could mainly crank the engine in this fault condition it would still start and run but since it's electric start only there's no way to crank it as it disables the starting switch solenoid circuit.

captain oblivious said:

I recently came to visit my daughter and she said her lawn mower will not run first I replaced the spark plug still no spark then I pulled the pull rope cover off and inspected the coil found that it was Rusty apparently been leaving it outside so I've replaced the coil clean the flywheel and still no spark any help would be appreciated

Click to expand...

No spark is only the result of coil, coil wire, spark plug, grounded kill wire. I've seen all these "brand new broke". It is very possible that the wire connection inside the plug boot isn't making contact with the plug connector. The coil has to orientated correctly. It only works one way, even though it can be mounted either direction. Gap is set with coil straddling the flywheel magnet at 10 thousandth. With kill wire disconnected it should produce spark, just won't shut off. Very common is kill wire insulation ate by mice.... anywhere it would touch engine block is ground and will prevent spark.