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Hello, I hope everyone is well.
I have a problem with my lawn mower that has completely baffled me. It's a 2015 McColloch M46-125WR with a briggs and stratton 450E engine. Earlier on in the year I replaced the carb as it was running very lumpy with more smoke than what should be normal coming from it and that worked a treat. Last week I was mowing and it gradually died (like it does when you run out of fuel).

At this point, I had a spark at the plug so as I had bought a spare carb at the time, I just put the brand new one on. It still wouldn't fire up. I then found there was no spark so I bought and replaced the coil. Still not firing up and still no spark! It had to be the small earth wire so I changed it. Still no spark! The magnets in the flywheel are fine too
I'm just wondering if anyone has ever came across this problem before and is there a fix? My logic tells me it should be working by now?

Thank you in advance

Unplug the kill wire (earth wire) from the coil and check for spark.
also, how did you set the air gap between the coil and flywheel?

And if you haven't already done it replace the spark plug. After 23 years in this business one thing that I have learned is NEVER trust a spark plug. Just too many odd issues that related back to faulty spark plugs.

Hi, thank you for the replies. I set the gap with a folded peice of paper as I can't find my guages (after points were no longer used on cars I thought I'd never need these again!). I'll try disconnecting the kill switch wire.

I tried 2 different plugs but I can grab one from the car and see if that works. Years ago we used to just put a screw driver in the HT cap to check if the coils were working

If none of this makes it work you might consider that the brand new coil could be defective. Did you check its resistance?

How exactly did you determine no spark?

I still have a dwellmeter in a toolbox, pining away for the day when I have a real car to work on again...

the trigger chips in the coils throw off resistance reading.
coils usually either
Work
Don't work
Work with the kill wire unplugged
Don't work when they get hot

New Chinese coil?

Scrubcadet10 said:

the trigger chips in the coils throw off resistance reading.
coils usually either
Work
Don't work
Work with the kill wire unplugged
Don't work when they get hot

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Except when they deliver a half-assed weak spark that won't pass the Slomo test. Like that infamous Ariens thread, or that fellow who confirmed spark by grabbing the plug wire but it turned out the points were burnt. Or my '92 that would give me a jolt but wouldn't catch until I replaced the coil. I'm guessing the cause is shorts here and there in the coil secondary windings; the wire is after all insulated with what amounts to dry spit.

Richard Milhous said:

Except when they deliver a half-assed weak spark that won't pass the Slomo test. Like that infamous Ariens thread, or that fellow who confirmed spark by grabbing the plug wire but it turned out the points were burnt. Or my '92 that would give me a jolt but wouldn't catch until I replaced the coil. I'm guessing the cause is shorts here and there in the coil secondary windings; the wire is after all insulated with what amounts to dry spit.

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Think you missed the point Richard
They can not be repaired so either they work or they get replaced

Hi folks,
I now have a new spark plug that sparks away nicely. Still not running though. I took the carb off and refitted the old one, It started for about half a second and then stopped. I have just blown down the fuel inlet on the new carb after blocking the air inlet and where the primer bulb should be and there's no air coming out at the part that joins the engine unless I blow quite hard.

MrGbo said:

The coil I bought was from Mr. Bezos website. It's description is "OuyFilters OxoxO Ignition Coil Compatible with 593872 799582 798534 Compatible with Briggs & Stratton 08P500 08P600 093J02 09P600 09P700". I borrowed a multi meter from my neighbour (I really need to get one of these) and tested both the new and the old coil. With the multi meter set @ 20k Ohms the original coil is coming back with a reading of around 8.87 so there was nothing wrong with it Same with the new coil too.
I detemined no spark by taking the plug out, plugging it back into the HT lead and leaning it against the block whilst I had the wife pull the cord.

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Are all the OEM Briggs coils gone now?

What's with Mr. Bozo and his "compatible" coils? Is this a Chinese clone coil?

Put the meter back in the drawer. Lock the drawer with a TIG welder. Coils either work or they don't. Wasn't this already covered on the last page?

Actually electronics don't throw off the resistance. The SMT board actually has a high resistance than coils primary which around 1.7 ohms. This because coil' primary winding directly to the kill tab and is grounded on the other end to the coil's metal core. The problem is you can't test the electronics. And BTW the Briggs coils are not using computer chip but SMT transistors, inductors, capacitors, resistors, and may be a diode or two. All mounted on a single sided circuit board.

The coil's transformer has a turns ratio 1 to 18 approximately.

If you're not getting spark, measuring resistance can confirm (but not completely rule out) the coil as a problem.

I thought the OP already tried multiple spark plugs???

Richard Milhous said:

If you're not getting spark, measuring resistance can confirm (but not completely rule out) the coil as a problem.

I thought the OP already tried multiple spark plugs???

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From what I've read, OP ignores suggestions and does his own thing.

slomo said:

From what I've read, OP ignores suggestions and does his own thing.

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I did actually try 2 different spark plugs earlier, sorry i forgot to mention that. I thought 2 spark plugs couldn't be defective but they were.

Two spark plugs were not defective, unless you pulled them both from a scrapyard. Test procedure, maybe.

MrGbo said:

The coil I bought was from Mr. Bezos website. It's description is "OuyFilters OxoxO Ignition Coil Compatible with 593872 799582 798534 Compatible with Briggs & Stratton 08P500 08P600 093J02 09P600 09P700". I borrowed a multi meter from my neighbour (I really need to get one of these) and tested both the new and the old coil. With the multi meter set @ 20k Ohms the original coil is coming back with a reading of around 8.87 so there was nothing wrong with it Same with the new coil too.
I detemined no spark by taking the plug out, plugging it back into the HT lead and leaning it against the block whilst I had the wife pull the cord.

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iF IT HAS A METAL SHIELD ON THE PLUG WIRE CAP, THE INSULATOR IN IT CAN CRACK AND THE THE SPARK JUMPS TO THE METAL SHIELD AND IS CONNECTED TO THE BASE OF THE PLUG AND NEVER GETTING TO THE GAP. tHEN YOU PULL OFF THE CAP AND CHECK THE SPARK WHEN THE METAL SHEILD CANNOT GROUND THE SPARK SO THINGS PASS THE TEST, THAT IS UNTILL YOU PUT THE CAP BACK ON THE GROUND BODY OF THE PLUG.

VRR.DYNDNS>BIZ said:

iF IT HAS A METAL SHIELD ON THE PLUG WIRE CAP, THE INSULATOR IN IT CAN CRACK AND THE THE SPARK JUMPS TO THE METAL SHIELD AND IS CONNECTED TO THE BASE OF THE PLUG AND NEVER GETTING TO THE GAP. tHEN YOU PULL OFF THE CAP AND CHECK THE SPARK WHEN THE METAL SHEILD CANNOT GROUND THE SPARK SO THINGS PASS THE TEST, THAT IS UNTILL YOU PUT THE CAP BACK ON THE GROUND BODY OF THE PLUG.

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I'VE NEVER SEEN ONE LIKE THAT CAN YOU POST A PIC?

I managed to sort it out. contaminated fuel. One of my younger kids thought water went into the fuel tank ?‍ I stripped and emptied the carb, emptied and refilled the fuel tank. Now it runs like a dream again.

Thank you all for your help.

Richard Milhous said:

I'VE NEVER SEEN ONE LIKE THAT CAN YOU POST A PIC?

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Something like these.

Thanks. That head must run damn hot to need a metal heat shield.

Richard Milhous said:

Thanks. That head must run damn hot to need a metal heat shield.

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We used to use them on some car models years ago where the exhaust manifold was at the front of the engine next to the plugs. Like this