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I have an 11hp powerbuilt briggs that had no spark... I bought a new coil and spark plug installed and engine didnt fire. I put my spark tester on the spark plug and no light. I put the tester on a near by shroud/head bolt on the head and the light came on which tells me the coil is good but the spark plug wasnt grounding so I put a little wire from that same bolt on threads of spark plug but the engine did not fire. I tested the spark plug with the wire on the threads and no light came on the tester. I moved the wire to the spark plug tip and attached the coil but engine still did not fire. Note that during all this I have tried all these procedures using multiple new spark plugs even old good spark plugs. I also have cleaned the threads on the engine block as well. I have checked all wiring and as well as coil kill wire. All looks good. The engine was a little loose so I snugged the mount bolts tight. Compression is perfect. I am literally so baffled on whats going... Has anyone had this issue? I also should note that when the plug tester is on a shroud/head bolt getting spark the light was very strong and not weak. Somewhere while testing I did notice the tester had a faint light while on the spark plug but not all the time. Only time the light tested strong was on shroud/head bolt or on the ground wire... even when the wire was on the tip of the plug but not when on the spark plug threads tightened into engine. Fyi the shroud/head bolt is not a head bolt it just screws into the head holding the shroud on. I made a YT video explaining better that I will post in comments once finished downloading.

check your ground straps & cables from engine to chassis by hand

What did you set the armature air gap at and how did you set it? Should be set at .010”.

mechanic mark said:

check your ground straps & cables from engine to chassis by hand

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Thanks ill try that and update. Having a break from it maybe it did have something to do with the loose engine grounding.

Rivets said:

What did you set the armature air gap at and how did you set it? Should be set at .010”.

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I have replaced many coils for customers and have always spaced them using two of my business cards which had never been an issue.

In my opinion two business cards is way too thick, timing is too late to generate a hot spark. I’ve changed a few coils over the years and .010” or one business card in a pinch is what I always recommend.

Rivets said:

In my opinion two business cards is way too thick, timing is too late to generate a hot spark. I’ve changed a few coils over the years and .010” or one business card in a pinch is what I always recommend.

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I have re-checked/adjusted the gap using my vlave gap tester and it did not help.

I am yet to see an engine with an air gap that does not fall between 0.008" to 0.0012".
A coil which will send a spark directly to the ground which has no resistance but not through the plug where there is a higher resistance is generally bad , too far away from the magnets or upside down.
More important from a diagnosis point of view , what in line tester are you using ?
a red neon globe one, a white globe one, a 3 point one , a sliding contact one ?

bertsmobile1 said:

I am yet to see an engine with an air gap that does not fall between 0.008" to 0.0012".
A coil which will send a spark directly to the ground which has no resistance but not through the plug where there is a higher resistance is generally bad , too far away from the magnets or upside down.
More important from a diagnosis point of view , what in line tester are you using ?
a red neon globe one, a white globe one, a 3 point one , a sliding contact one ?

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I am using Part number "#20610 Lisle inline spark tester" on Amazon. Its always worked great testing and diagnostic the past 5 years.

Thank you.
All that your tester does is confirm that you have a voltage going from the lead to ground, it does not indicate how strong that voltage is.
I think they are good for anything above 100 V.
I would first of all check that the coil is properly grounded & fitted right way up.
A lot of them have a visible ground wire that goes to one of the mounting bolts.
Upside down most will either not work at all or produce a very weak spark
Polish the spot where the mounting bolts clamp down on the coil & also the underside of the mounting bolts & the tabs that the coil mounts on.
You can not have too good a ground contact or too many of them.

On most mowers the primary coil resistance is meaningless as it includes the trigger chip but the secondary ( laminations to plug cap ) will let you know if the coil is bad or the lead is bad.

After that you are left with the air gap and the magnet strength.
A good magnet will pull a screwdriver blade from about 1" away

Just watched your video, which I normally don’t do, and see some concerns. First, get rid of that ground wire you are using. Absolutely no need for doing any tests. Second, you don’t say whether you reset the armature air gap to .010”. Third, remove the kill wire from the coil. Now, plug your spark tester into the coil wire and hold the other end to a good ground on the engine. Turn the engine over, do you have spark? NO, bad coil. YES, proceed. Now attach the spark tester to the plug. Turn the engine over, do you have spark? NO, bad coil. YES, proceed. Reattach kill wire to coil. Turn the engine over, do you have spark? NO, bad kill wire. YES, engine should start. Report back results.

Rivets said:

Just watched your video, which I normally don’t do, and see some concerns. First, get rid of that ground wire you are using. Absolutely no need for doing any tests. Second, you don’t say whether you reset the armature air gap to .010”. Third, remove the kill wire from the coil. Now, plug your spark tester into the coil wire and hold the other end to a good ground on the engine. Turn the engine over, do you have spark? NO, bad coil. YES, proceed. Now attach the spark tester to the plug. Turn the engine over, do you have spark? NO, bad coil. YES, proceed. Reattach kill wire to coil. Turn the engine over, do you have spark? NO, bad kill wire. YES, engine should start. Report back results.

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Okay so the engine fires when the Kill wire is disconnected. I believe that would be a bad ignition?

No, it means the kill wire is grounding out somewhere. Either the wire is frayed or is not attached properly at the kill switch end. This is located where you bail cable is attached to the engine.

I rarely watch videos either as we have rubbish internet down here & have very limited downloads.

Firstly if you are going to play at repairing mowers please do some basic learning.
Lots of "how to" books that explain how things work.
1) the wire that you are calling a ground wire on the coil is the kill wire
When running it should be open circuit , no voltage & no ground

2) the spark plug IS A GROUND CONNECTION for the coil with a gap in it so the electricity has to jump across the gap .
Putting a wire on the top of the plug simply makes another ground connection bypassing the spark plug gap.

In a electrical circuit, an air gap is a resistance, the bigger the gap the higher the resistance
The higher the resistance the more voltage is needed to overcome it.

So if you connect your tester directly to the engine by putting a BYPASS JUMPER on the top of the spark plug and it lights up but it will not light up when connected to the spark plug the output voltage of the coil is too low to jump the gap.
Electrically with that wire there it is the same as putting your tester between the HT wire and the block.
If you get some really old mowers in for repair you will see a tab that sits over the spark plug which the operator pushed down onto the spark plug to stop the engine by bypassing the spark plug.

There are 5 reasons for a coil which will light up to the block but not through a good plug.
1) wrong coil
2) coil on upside down
3) magnets weak
4) coil air gap too large
5) bad ground connection between the coil and the mower