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Hello,
My son mows the lawn, so yeah, had to replace the flywheel key when the cord damn near pulled my arm off. After key replacement, the mower sputtered, ran a second or two, and then stopped. Replaced the carb with a new one, drained the fuel, drained the oil, checked for spark (yep), took off exhaust/muffler and put back on, tried starter fluid, spun the blade to check for compression (definitely has compression, but how much I can't measure).

I do not know where to go from here. My only thought is to take the bulb off the new carb (from China, 10 bucks) and see if perhaps there is crap in it.

Thanks for any help!

Did you torque the fly wheel bolt/nut when you replace the fw key. If not it would probably cut the key again. If the fw key is cut it will still have spark since the key has nothing to do with whether it will have spark or not. It just times the spark to the right time when the piston is at tdc on the compression stroke. It will also fire on the the exhaust stroke. As long as the magnet on the fw pass by the ign module it will fire.

Was the flywheel properly torqued after replacing the key. Could of sheared the key a second time.

Thanks hlw49 and ILEGINE. I'm not sure exactly how to torque it, but I did tighten it. After trying to start it numerous times, I undid my previous work and checked and the flywheel key was still in the same place. I put it back together and kept at it, but I haven't checked after the last 40 pulls
To torque it, do you recommend just extending the handle of my ratchet?

Torque to 55 lb/ft or 74.5 Nm

You need a torque wrench. Many auto part stores have a loan a tool program. Just using a ratchet will tighten the retainer but you will not how pressure you are applying and can easily damage flywheel taper or even bust it.

you may need a tool to hold it from turning too. Check the blade to see if it is loose. Also double check the coil air gap if it is that style coil. I don't understand about the cord "pulling" your arm off unless you mean it back fired and tried to spin backwards.

sgkent said:

you may need a tool to hold it from turning too. Check the blade to see if it is loose. Also double check the coil air gap if it is that style coil. I don't understand about the cord "pulling" your arm off unless you mean it back fired and tried to spin backwards.

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Exactly can happen with a sheared flywheel or ACR failure. I had Honda GX390 actually jerk back so hard that I had nearly dislocated fingers. Not a fun thing to happen especially you depend on your hands to make a living.

And he will need a tool to keep the flywheel from turning. Blocking the bar blade can work many times on walk behind as long as the blade is not clutched.

Hello all, thanks for your help. I'm embarrassed to say it was the spark plug. The old plug had good spark. I checked it twice! Anyway, since I had replaced everything else, 5 bucks for a new plug seemed like a good idea. I put in the new plug and it started on first pull and ran like brand new. Hopefully someone can learn from my mistake. I do need to torque the flywheel nut though, but at least I can knock down my 10 inch grass before the HOA comes complaining.

GitPicker said:

Hello all, thanks for your help. I'm embarrassed to say it was the spark plug. The old plug had good spark. I checked it twice! Anyway, since I had replaced everything else, 5 bucks for a new plug seemed like a good idea. I put in the new plug and it started on first pull and ran like brand new. Hopefully someone can learn from my mistake. I do need to torque the flywheel nut though, but at least I can knock down my 10 inch grass before the HOA comes complaining.

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One thing that I have learns in my many years of repairing mowers is never trust the spark plug.

Modern fuel is conductive at cylinder compression pressures
Modern fuels will leave an oily residue on the spark plug nose
Electrical resistance increases with pressure .
So it will spark beautifully in open air but in the engine spark will track down the side of the plug following the path of least resistance
This is why you hear that a good magneto will throw a 1/4" to 1/2" spark ( or better ) outside the engine yet the gap is only around 0.030".

ILENGINE said:

One thing that I have learns in my many years of repairing mowers is never trust the spark plug.

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I was recommended this plug for my Briggs engines by a pro mower guy. He says it is way more resistant to carbon fouling and misfiring. He has a gang of summer workers that are NTB and will over-choke an engine until it starts to sputter and sputter and foul a regular copper plug. I have had no starting issues but wonder if it's a worthwhile upgrade?

@SamB The problem with the plug isn't direct fouling. The problem is the porcelain is not sealed and gas is conductive at combustion pressures. The gas soaks into the porcelain causing internal shorting of the components.

ILENGINE said:

@SamB The problem with the plug isn't direct fouling. The problem is the porcelain is not sealed and gas is conductive at combustion pressures. The gas soaks into the porcelain causing internal shorting of the components.

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This is the reason for those "bad out of the box" spark plugs you occasionally hear
Every spark plug is tested at least 8 times before it is put in the box so every one is good when shipped.

ILENGINE said:

@SamB The problem with the plug isn't direct fouling. The problem is the porcelain is not sealed and gas is conductive at combustion pressures. The gas soaks into the porcelain causing internal shorting of the components.

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Is this just another case of cost cutting,buyer be damned? Glazing the porcelain would add to the cost so why do it if the plug will last a season! As for me, I'm happy with my Briggs and Stratton branded spark plugs.

SamB said:

Is this just another case of cost cutting,buyer be damned? Glazing the porcelain would add to the cost so why do it if the plug will last a season! As for me, I'm happy with my Briggs and Stratton branded spark plugs.

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Part of it may be cost cutting, but it came about due to fuel injections engines. the different environment of fuel vaporization made the need for sealing the ceramic porcelain less necessary.

And I have replaced more Briggs branded plugs due to failure than any other plug that I have come across The year they came out with the engines that used the .020 gaps I was replacing plugs in customer mowers about once a week.

SamB said:

Is this just another case of cost cutting,buyer be damned? Glazing the porcelain would add to the cost so why do it if the plug will last a season! As for me, I'm happy with my Briggs and Stratton branded spark plugs.

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Nothing what so ever to do with cost cutting.
All about badly written pollution laws and much more sensitive equiptment .
Pollution laws state 0.000% lead in exhaust gasses
The only glazes that will withstand engine conditions are lead based so they can no longer be used on spark plugs .
Now 30 years ago when the laws were written you could not measure lead in exhaust emission down to the 3rd decimal place
Now days we can do it down to the 6th decimal place
So when the laws were written the best we could do was 0.00%
I used to do metal analysis & health monitoring was part of the job
When microwaves came in some of the workers who never showed any lead pick up started to have lead in their urine
Th reason was they reheated old tea in their white porclean cups ( imported from Mexico ) and the glaze on the cups was lead based
so heating in a microwave liberated the lead .
For the fun of it we tested all of our own crockery and yes all of them infused lead into the tea , both the cups & the teapots
So from that day on nothing went into my microwave that was not in a glass container

ILENGINE said:

Part of it may be cost cutting, but it came about due to fuel injections engines. the different environment of fuel vaporization made the need for sealing the ceramic porcelain less necessary.

And I have replaced more Briggs branded plugs due to failure than any other plug that I have come across The year they came out with the engines that used the .020 gaps I was replacing plugs in customer mowers about once a week.Y

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Your favored plug for the 500cc briggs is what? A good spark plug eases the strain on everything on the engine,starter,battery,me. :-D

SamB said:

Your favored plug for the 500cc briggs is what? A good spark plug eases the strain on everything on the engine,starter,battery,me. :-D

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I try to avoid anything related to Champion. Have had to throw away complete cases due to immediate failures after installation. And The Briggs plugs are made by Champion. I prefer NGK, but they are not perfect either. My NGK failures have been less in 20 years of use than the Champion plugs I have had fail in one week.

I prefer the B2LM/BR2LM for the flat head engines and the BKR5E for the OHV engines in both Briggs and Kohler.

Unless specified by the customer they get NGK's because they are 50¢ cheaper & I charge the same price for all plugs.
NGK's also come in 10 packs & Champions or Bosch come in 4 packs or 10 x 4 packs
Same grades as Illengine unless there are signs of the engine needing a hotter plug.
OTOH
No 1 rule in engineering " if it ain't broke, don't fix it "
As such I would be lucky to change more than 20 plugs a year out of 300 or so jobs
I expect 50,000 to 100,000 miles out of my car plugs
I have plugs in engines that have not been changed since they were made and some of them are near 100 years old from the days of 2 piece plugs .

bertsmobile1 said:

Unless specified by the customer they get NGK's because they are 50¢ cheaper & I charge the same price for all plugs.
NGK's also come in 10 packs & Champions or Bosch come in 4 packs or 10 x 4 packs
Same grades as Illengine unless there are signs of the engine needing a hotter plug.
OTOH
No 1 rule in engineering " if it ain't broke, don't fix it "
As such I would be lucky to change more than 20 plugs a year out of 300 or so jobs
I expect 50,000 to 100,000 miles out of my car plugs
I have plugs in engines that have not been changed since they were made and some of them are near 100 years old from the days of 2 piece plugs .

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My truck plugs burn out and start causing issues around 40,000 miles. Oh guess what they are OEM Champion plugs. Because they are an OEM only available through the dealer plug.

Yes plugs can spark outside the compression zone but under compression fail to fire. I had one air compressor years ago that would run fine and build up pressure. It just wouldn't restart if the air was full and it turn out to a bad plug. It had me nearly pulling out my hair as to the cause.

Bert, Most of the NGKs I buy here comes 4 packs. Now some do come in 10 packs but they are usually the 2 cycle plugs.

And IL I have a lot failures of the 10mm CMR series NGK plugs which I am replacing with Bosch plugs but in the long run most plugs are fairly reliable.

Even new plugs can fail straight out of the box.

bertsmobile1 said:

Unless specified by the customer they get NGK's because they are 50¢ cheaper & I charge the same price for all plugs.
NGK's also come in 10 packs & Champions or Bosch come in 4 packs or 10 x 4 packs
Same grades as Illengine unless there are signs of the engine needing a hotter plug.
OTOH
No 1 rule in engineering " if it ain't broke, don't fix it "
As such I would be lucky to change more than 20 plugs a year out of 300 or so jobs
I expect 50,000 to 100,000 miles out of my car plugs
I have plugs in engines that have not been changed since they were made and some of them are near 100 years old from the days of 2 piece plugs .

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I don't just change my mower plugs out of boredom. Like you,bert,if it ain't misfiring or hard to start,I leave the plug alone!