Spark plug not grounding??

[joec1234]

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.

 

[mechanic mark]

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

 

[Rivets]

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

 

[joec1234]

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

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

 

[joec1234]

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

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

 

[Rivets]

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.

 

[joec1234]

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.

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

 

[bertsmobile1]

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 ?

 

[joec1234]

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 ?

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

 

[bertsmobile1]

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