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Mower won't start - No Spark.

We changed the Spark Plug, Still no Spark.

We changed the Magneto - We have Spark! (For a day)

Now, we have Spark from the Spark Lead when we ground it, BUT no spark with Any new Spark Plug.

Plugs check out fine with a Multimeter. It's almost as if there isn't enough power to make them spark though.

Could the Magnet in the Flywheel not be working as it should?

What about the air gap, is there any rust on the flywheel. make sure coil has good ground to engine block.

Spark Gap is set correctly to the measurements listed in the Service Manual.

No major rust on the flywheel.

All the grounding points for the coil are shiny and clean.

What about air gap on the coil.

Do you have the kill wire connected ?
If so remove it and try again.
Spark returns = short in the kill wire of switch.

EngineMan said:

What about air gap on the coil.

Click to expand...

I think I'm just unfamiliar with this term. Is that the space between the Coil and the Flywheel Magnets? - If so, It's set to .012"

bertsmobile1 said:

Do you have the kill wire connected ?

Click to expand...

The same issue with the kill wire disconnected.
Lead will spark, Plugs won't.

Dazza where did you take the kill wire off from ?? The coil itself..........?

Boudreaux In Eunice La. said:

Dazza where did you take the kill wire off from ?? The coil itself..........?

Click to expand...

Yeah, It just has a little Push-on connector for it.

Seems like you have a bad coil......... Try a known good used one......

Now for the burning question,
Did you buy the replacement from a mower shop, a real retail outlet or a pretend on line shop ?
Ever wondered what happens to all the parts made in cheap labour countries that fail the QC testing for Briggs /Kohler / Honda etc ?
They ultimately end up on the site of an on line seller at an unreal low price, truthfully advertised as OEM part, they just neglect to tell you that they are quality control failures.
If it came from a mower shop take it back and ask them to test it. If the counter staff go red in the face then slink off like a sly dog & give you a replacement, naked then it is a knock off of dubious quality.
Good ones come in branded boxes ( or bags ) and will have both a part number and batch / serial number on them,.

It's a Genuine Briggs&Stratton coil from a mower shop.

The old coil stopped working, which is why we got the new one.

But I'm wondering now, if the Magnets in the flyweel could have gone a bit bad. - If they are not as strong as they should be, wouldnt they create less power in the coil?
(thinking that the older one would have been affected first because it's older, new one, because it's newer and would be in better condition was able to run for a short while? but not it cant either.)

DazzaJay said:

It's a Genuine Briggs&Stratton coil from a mower shop.

The old coil stopped working, which is why we got the new one.

But I'm wondering now, if the Magnets in the flyweel could have gone a bit bad. - If they are not as strong as they should be, wouldnt they create less power in the coil?
(thinking that the older one would have been affected first because it's older, new one, because it's newer and would be in better condition was able to run for a short while? but not it cant either.)

Click to expand...

Yes the magnets could be weak, and you did ask that in your first post......

You did say that the mounting areas were shiny...... What I do to make sure is I take a flat file and rub it across the mounting posts VERY LIGHTLY and then take a brass wire wheel on a cordless drill then clean the coil surfaces where they meet the posts and the legs that face the flywheel.........

Then I spray with carb cleaner and blow dry with a air gun or let sit a few minutes in the sun....

Yes I have seen magnets go bad on older chainsaws and a few Briggs engines.... So your magnets maybe are bad....

Clean the flywheel mags with a brass tooth brush and spray some carb clean then try that........ Also the file trick that I said earlier.........

Let us know Mon Ami ~!~!

You never did say you had a Briggs engine or the model number........

What is your engine model number by the way ???

Also is it a rider mower ????? You said you had spark for a day........ If you have a rider mower then you might have zapped the coil with some stray voltage some kind of way ..........

Yeah, She's a Rover Ride-On Mower.
and she looks quite old.

It's previously had a complete re-wiring done on it (A few years ago).

And the Engine is a Briggs&Stratton:
Model: 257707
Type: 0129-01
Code: 92021011

Coil (armature) part number 398811 air gap .014 valves gap In.005 Ex.009

While it is very rare, the magnets can go weak particulalry it the magneto legs ( or something else ) has been rubbing on them.
If they are in good conditiion they should cause a screwdriver to pull in from 1 " out.
The coil itself could be leaking.
Try spinning the engine late at night in a dark place and look for sparks around the coil running across the surfaces,

Dazz a business card is 12 to 14 thou.... My cards are 13 I think..... That's what I use to gap my coils with.... My service tags are 11 thou and that's what I use for the small 2 to 4 HP engines......

Years ago I had all different coil gap gauges but when I sold out all that went with the inventory...... I wish I still had half the stuff I had back in the early 90's and late 80's...........

Bert gave you some great advice on the leaking coil.....

Let us know Mon Ami ~!~!

I've had the local small engines guy have a look at it last night, and even he's confused.

he's described it as a "very weak spark" and he's currently looking to see if he has a spare flywheel laying around, as he's thinking Magnets too.

Ok.... It's solved. and it's stupider than we imagined.

It was the Coil. (Both the original and the Genuine New Replacement)

So, Let's go through the entire list of how we came to this conclusion.


No Spark.
Replaced Spark Plug. Sill no Spark.
Replaced Spark Plug Again. Sill no Spark.
Replaced Coil & Lead with B&S Genuine Replacement. Still no Spark.
Replaced Flyeheel. Still No Spark.

So, from this point we decided to work backwards from the flywheel. Seeing as we already forked out for an expensive B&S Genuine Coil, we instead ordered in a cheapo chinese one...

Replaced Genuine Coil with Cheap Chinese Coil.
IT WORKS!

Which means, When the engine first failed, it was the Coil at Fault. and when we replaced it with a Genuine B&S Coil, the Replacement from B&S Must have been Dead On Arrival.

What a bloody headache that was. now to get a refund on the genuine B&S Coil that doesnt work.....

Coils do come in DOA, but I have never seen one.... I have heard of it though....... Sometimes on a rider mower as in a older one positive voltage can get to the kill wire and zap the coil right away.......

If the same thing happens in the future then you will need to check the wiring on your unit.......

Briggs has a very stringent QC system, but a bad coil coil can get thru.....

Plus Tard Mon Ami ~!~!

BTW that's why I mentioned in an earlier post to use a good known coil from a used mower........

Let us know if something goes awry ...........

Check that cut off wire to the coil.
If it shows any voltage under any condition it will fry the Hall Effect trigger chip inside the coil.
Some of them are more tolerant than others.
Testing the coil with a cheap meter can in fact fry the chip as well.
Not much chance of a refund.
Briggs Australia is even tighter than Briggs USA.
As of today Briggs have taken over the distribution of Oregon products so if you have any Oregon products forget about getting parts for them, or uncommon chains or bars.
Expect to see lots of Oregon branded ( Chinese made ) battery stuff in stores where "lowest prices are Just the beginning" ( of your problems ).

bertsmobile1 said:

Now for the burning question,
Did you buy the replacement from a mower shop, a real retail outlet or a pretend on line shop ?
Ever wondered what happens to all the parts made in cheap labour countries that fail the QC testing for Briggs /Kohler / Honda etc ?
They ultimately end up on the site of an on line seller at an unreal low price, truthfully advertised as OEM part, they just neglect to tell you that they are quality control failures.
If it came from a mower shop take it back and ask them to test it. If the counter staff go red in the face then slink off like a sly dog & give you a replacement, naked then it is a knock off of dubious quality.
Good ones come in branded boxes ( or bags ) and will have both a part number and batch / serial number on them,.

Click to expand...

Great point. There is a multi billion dollar business in counterfeit products! I work for Kemet Electronics. We make triple redundant capacitors. They are made using tantalum which is actually a metal that can hold a charge. We make them for defense, private and public satellites and the ISA. I was in China a while back and a coworker and I found this huge electronics mall. We went into one shop and they had rolls of Kemet's capacitors. They were counterfeits! They were also priced much lower. Tantalum is about 150 dollars a pound. We could also see that they used a video jet to print the information of the capacitors. We laser etch that information.

Yep.
Some flag waving, church going, American born , patriotic, fine upstanding, community member went over there with some of your products and said, "can you make me 1,000,000 that look exactly like this , really cheap cheap ? "
And that is exactly what the factory did.
Except they made 2,000,000 of them and sold the rest into the general market.

People like to think that those nasty, thieving, slanty eyed, devils send spies over to the USA ( or Aust or the UK or Germany ) to steal our great products and make counterfeit ones.
But that is not how it works.
The factories make what they get paid to make.
Only problem is once set up to make your stuff, nothing to stop them making a lot more .
Down here retail chain shops commission counterfeit products in order to dupe the general public that they are getting exactly the came product as the locally made one that sells for $ 200 for $ 50 .
And because people are the most stupid species on the planet, we buy it without thought then it breaks so we go buy a different product because the one we bought looked exactly like the expensive local one so that must be trash as well/.
Thus the local company goes broke and the quality products vanish forever.