Ariens Briggs & Stratton won't start.

[Richard Milhous]

a healthy spark should be able to jump the 1/4" gap... think of it as a load test... as it has to over come immense compression in the cylinder.

Technically, it's not the pressure, it's the density. Air is an insulator; hydrocarbons are even better insulators. Increase the density by 6x or 8x, and you increase the resistance the spark has to cross. It's more complicated than this, because vacuum is also an insulator, and the temperature increase caused by compression will reduce the resistance, but I'm guessing 1/4" gap is a real good approximation of the resistance that spark has to beat.

Trivia: the spark you actually see is wasted. Ignition is caused by the invisible capacitive discharge over the gap, which ionizes the air. The visible arc is inductive discharge over now negligible resistance, which adds very little to the arc temperature. It eats the crap out of points, though, which is one reason they use a condensor to absorb that current.

 

[D_H]

a healthy spark should be able to jump the 1/4" gap... think of it as a load test... as it has to over come immense compression in the cylinder.

I've asked a few times about the ignition coil after testing the spark. So you're thinking it's bad it seems? Your recommendation, based on everything I've done, is to replace the ignition coil?

 

[D_H]

Well the post is starting to become a War & Peace length novel and reposting what you put in the original post does not help as we recognise it and bypass it.
Some people see your post as a thread while other who use phones will only see a series of emails so it is hard for them to follow the entire thread as it gets broken up by all of the rest of their normal email traffic .
If you have compression of a volatile fuel in a ratio that will ignite at that compression & a spark to ignite it then the engine will start & run.
In a situation like yours, ignoring all that has previously been said I start by getting a known good plug from a running engine .
remove the blower housing
By & large , while I listen the what the customer tells me I ignore it as by virtue of the fact the mower is in my shop their work is suspect .
Step 1
Put a short shot of starting fluid ( carb cleaner ) down the plug holes replace the plug & hit the starter
Goes bang = vales are closing , spark is good & at the right time. Go to step 2
Does not go bang the I remove the kill wires from the magnet & repeat
Goes bang = faulty wiring
Does not go bang = faulty magneto

Step 2
Repeat step 1 with customers plugs
Goes bang = plugs OK
No bang = faulty plugs
NB modern fuels are light oil with just enough volatiles to start a cold engine
IT IS HIGHLY CONDUCTIVE AT COMPRESSION PRESSURES so if it damps a brand new plug, the spark will track down the sides & not jump the gap.
The only way to remove this coating is to burn it off .
This is the "bad in the box" syndrome you keep hearing about because brand XYZ plugs are crap .

Step 3
Spray a SHORT SHOT of starter fluid down the carb ( Choke wide open ) close the choke and crank the engine
Goes Bang Bang Bang then valves are working properly & problem is with the fuel supply.
Does not go Bang = valve / cam problem

Enough typing from me for now.
If you wand my help then do EXACTLY what was asked and post the results
Telling me you did this last Sunday week is not good enough.
I need to know the answer as it happened today, not last week.

And sanding the coil & flywheel does more damage than good unless the rust is so thick that the coils touch the magnet as it passes.
Sanding the mounting posts so there is a know good ground is all that needs to be done
The kill wire terminal is self cleaning so the act of removing & replacing it will have cleaned it well enough.

I agree that this is turning into a novel. It's turning into a novel for a few reasons:

• I have to repeat myself to posters.
• Posters will not read what I post.
• Posters can not remember what I've done.
• Can't remember what mower I've got.
• Can't remember what I've done in this thread.

I get some of that. I am trying to make this as easy for people as possible have all of the current information in one place, instead of all over this thread, since people don't want to read or remember. You're going to prove my point in this next part.

Oh, and I guess I'll have to try to guess what NB to you means. No bang? Man, my fingers hurt now.​

We get emails, life is tough...​

That is why I reposted what has happened. If you'll try to notice this time, there are more 'things I've done' in the reposting than in the original posting. In the reposting I've included what has transpired in this thread so as to make it a little easier for people.

I believe you when you say you ignore people.

Ariens Briggs & Stratton won't start.

Have you tried more "starter fluid" while starting?

www.lawnmowerforum.com

In reading your reply, I realized I forgot to mention a moment ago, again, that when I had the spark plug out, I sprayed at little carb cleaner into the hole, and when I reassembled the plug and attempted to start, the engine did try to fire. About two bangs starting on the first revolution.

As far as plugs go, again already in the thread, I am using brand new plugs. Brand new one (I list what it is on page one) in the engine, and a brand new one used to gap 1/4". I have already said I sacrificed that plug.

As far as your help, no, if you are not going to take this seriously, then don't reply. Retorts like yours are some of the reason this thread is long. If you want to be helpful, be helpful. I've got a mower that has been working like a brand new machine for the past 8 years running, until a week ago. I don't need to be answering the same questions again and again, or providing the same information over and over, or trying the exact same things over and over because people can't read. You're wasting my time.

 

[Richard Milhous]

Slomo told you long ago how to test your spark. You didn't bother. Now that it failed the test, you're still farting around.

You whined about 5 (not totally irrelevant) posts hijacking your 200-post thread.

You can't be bothered to find non-ethanol gas.

You won't drop $30 on No-Reilly for a compression gauge, but you expect total strangers to judge your engine compression by telepathy.

Just take it to a shop.

 

[D_H]

Slomo told you long ago how to test your spark. You didn't bother. Now that it failed the test, you're still farting around.

You whined about 5 (not totally irrelevant) posts hijacking your 200-post thread.

You can't be bothered to find non-ethanol gas.

You won't drop $30 on No-Reilly for a compression gauge, but you expect total strangers to judge your engine compression by telepathy.

Just take it to a shop.

I could go back and show you where and how you are wrong on every single one of your statements. But I'm not wasting that kind of time.

You think you're frustrated...it's my mower.

 

[Scrubcadet10]

i would say the coil is definitely a suspect and should be held for questioning... With a good ground it should throw a spark 1/4".... Reading back you said it did not fire with starting fluid down the intake, but it did fire with starting fluid down the plug hole that would make suspect the intake valve not opening, but you also said you could see some fuel shooting out of the plug hole when you were checking for spark so that suggests the intake valve is opening properly. A real head scratcher you have here.
When it died, did it cut off like when you turn the key or did it sputter like you would have ran out of gasoline.

 

[bertsmobile1]

If you follow what I posted you will recognise the diagnostic process works by bypassing things one at a time.
So it is important that the goop down the plug hole step one is done again as with all of the faffing around by now your new plugs could be compromised.
Then followed by step 2
I use terms like "Bang & No Bang" because they can not be misinterpreted as some will call a spark jumping a gap "fire " etc etc etc.
I could have said combustion but I like to keep things simple.
And with mowers they are simple and way too many people try to make things a lot more complicated than they should be .
If the magneto is strong enough to ignite the goop down the plug hole and then in Step 3 to ignite the goop sprayed into the carb throat then it is strong enough to start & run the engine, even if it misses a bit so it really does not matter if it throws a 1/8 " spark, a 1/4" spark , a 1/2" spark or even a 1' spark just so long as it ignites the fuel .
I have 5 different spark testers , the trick is to use the one that is appropriate for the diagnosis you are trying to do .
I saw where this thread was going so decided not to get involved as I am a mower technical & not a novelist.
Even more so with magneto coils because they are a works or replace item & not repairable.
Once the engine is running we can worry about the spark strength or lack there of which will manifest itself as a miss .
Right now the immediate problem is getting the thing to start.
So back to what I posted before
If you want my help then please do the tests as posted then post your results from each one .

On another "war & peace" it got to page 8 before the owner posted that the rockers were at different heights so we finally worked out the valve guides have shifted.
What I asked you to do tests the basics.
I should also have mentioned we need to know where the engine went bang
Ie in the exhaust = valve open or timing wrong
in the carb = valve open usually because of a loose seat .

So over to you.
I am off to do a house call & replace a deck belt so won't be back till tomorrow local time.

 

[slomo]

I have pulled the (new) spark plug out and rested it on a frame screw while the plug is plugged into the spark plug boot. The spark plug sparked every time. I gapped a different (new) plug to 1/4" and did the same test. That plug sparked a few times only, most of the time nothing.

Make sure the part is clean and rust free that you ground the plug to. No paint just clean metal.

 

[D_H]

i would say the coil is definitely a suspect and should be held for questioning... With a good ground it should throw a spark 1/4".... Reading back you said it did not fire with starting fluid down the intake, but it did fire with starting fluid down the plug hole that would make suspect the intake valve not opening, but you also said you could see some fuel shooting out of the plug hole when you were checking for spark so that suggests the intake valve is opening properly. A real head scratcher you have here.
When it died, did it cut off like when you turn the key or did it sputter like you would have ran out of gasoline.

Yes, you are correct on your reading. That's exactly what I have done and that's exactly what the mower did.

Yes, when the mower shut off, I started it up, I was driving it out of the garage, across the driveway to grass, (with the blades not engaged) the mower shut off, just like if I had either 1) turned the key off, or 2) stood up off the seat while the blades are engaged. Yes, it just turned off. No sputtering, no surging, just off.

 

[D_H]

Wait a minute. I'm not a mechanic. I'm doing the best I know how with this.

I am just now reading that I need to make sure the grounding screw is free of paint. I didn't know that. Some of the paint has worn off but it still has some paint. I'll go take a wire brush to it to remove the rest of the paint.