B&S flywheel magnet question

11 years ago

I have a toro walk behind mower with a B&S mower that won't start up. Was working fine all year. Started on the 1st or 2nd pull too. changed plug, oil, filter, gas. Checked carb, no deposits in it. Pulled the plug and visually inspected for spark. A faint spark under no load. So pulled off the shroud and checked the ignition coil. I tapped the 1st magnet on the flywheel with a screwdriver and it stuck on. The magnet on the other end, the screwdriver wouldn't stick on. Tried it with something lighter and it barely stuck on. Is the flywheel supposed to have one strong and one weak magnet?

Featured Answer

Greg Goyeneche

11 years ago

Briggs hasn't used a two-magnet flywheel since the late 1960's. The two-magnet flywheel was matched with a three-leg coil. Since then all Briggs aluminum engines have had a single magnet and a two-leg coil. Since 1983 magnets have been the same but coil is now electronic (magnetron) with transistorized triggering.

Don't know what you've got since you didn't post any engine numbers. Hard to help you any further without these numbers.

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Comments (6)

georgepuli
Original Author
11 years ago
My bad. It's a Toro mower with a B&S engine, # is 125K02-0189. The flywheel seems to have two magnetized sections, and one section has a strong pull, and the other (diametrically across the wheel) has a weak pull. The original flywheel part # is 692315, which B&S has since replaced with # 691987
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Greg Goyeneche
11 years ago
There is only one magnet in the flywheel. The other piece of steel is a counterbalance and may have only picked up some residual magnetism. If you've got strong magnetism in the one piece, your flywheel is good.

It's possible that your ignition coil is bad. The B&S part number is 802574. OEM part is about $35 to $40; aftermarket ranges from $20 to $25. The proper install is to gap .010 over the magnet. A business card works as a pretty good shim.

Before you replace the coil, disconnect the kill wire from the coil and see if you get good fire. Keep in mind that the spark will be weak at cranking speeds, and doesn't produce a strong spark until 250rpm or so.
georgepuli thanked Greg Goyeneche
georgepuli
Original Author
11 years ago
Awesome. Thanks. Will report back with what I find. I also haven't checked if the wheel key has sheared, so will check that out as well
romore_gw
11 years ago
The key does not affect spark on the Magnetron equipped engines, only the timing. This threw a few of us for a loop when the change was made from points style ignition.
georgepuli
Original Author
11 years ago
Update : it was the coil. Didn't even check the key as I didn't have the tools to take that assembly apart. Ordered a new coil online and installed it and it started on the first pull. The old one lasted 7-8 years, and was rusted all over. Thanks to everyone for your help.