# Twin cylinder briggs and stratton not firing on 1 side



## whitecloud20xx

Hi I have a Murray riding mower that a friend of mine put a rebuilt Briggs and Stratton engine on twin cylinder and it was working fine and then the magnetron stopped working so I replaced it and I am only getting spark on 1 side. I have checked every possible thing I could think of and can't seem to figure it out


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## jrrdw

Is this 1 coil with 2 leads or 2 coils?


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## whitecloud20xx

It has 1 coil with 2 leads brand new installed correctly and new spark plugs.


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## jrrdw

Are you certain that cylinder is getting gas? Put a little bit in through the spark plug hole and try it. It's a possibility it wasn't the coil that malfunctioned.


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## whitecloud20xx

It is getting fuel and air and has good compression I am testing for spark and not getting spark on the one side. I have checked the ground wire as well.


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## jrrdw

Spark plug lead bad???


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## whitecloud20xx

Magnetron ignition leads are new with coil.


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## BenHolliday

swap plug wires and see if it changes sides... maybe the cables


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## whitecloud20xx

The spark plug wires are part of the coil


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## jrrdw

Does the compression in both cylinders seem equal?


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## whitecloud20xx

Compression is good. If you test spark outside of the cylinder you get good spark on one side of the coil and not a thing on the other.


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## jrrdw

Are both the triggering magnets still in the fly wheel? Are they clean? Touch any piece of steel to both of them and make sure they are equal strength or close to it.


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## whitecloud20xx

Yes they are there and work fine.


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## jrrdw

That's everything I can think of...


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## whitecloud20xx

Alright I think the magnet on the flywheel is bad but the dealer around the corner says they don't sell just the magnet for the flywheel, I would have to buy the whole flywheel which is 200 some dollars. Does anyone know where I could get a magnet that would work?


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## K-B

You can't replace the magnet separate from the flywheel. It is extremely rare for the magnet to fail. I would say you get a defective coil.


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## whitecloud20xx

6 coils later it is not the coil or anything else it is the magnet it is weak and you can take the magnet off so why don't they sell them?


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## K-B

I didn't know this was the 6th coil. In that case, there must be something else wrong (besides the coil). What are the model, type and code numbers for this engine?


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## whitecloud20xx

IT is 422707 12174 01 and 90031512. I have checked compression and the wiring harness, the magnet isn't working like it used to the magnetism is in the plate that is in between the two sides of the trigger magnet and the magnet doesn't hold anything.


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## jrrdw

If I remember correctly the trigger magnets are held on by a #3 Phillips head screw. Here's a test, switch the magnets and see if the other cylinder fires...if it does you found the problem. A lot of junk/scrap yards have a stash of old lawnmowers and maybe you can find a used fly wheel. Also keep your eye on Ebay, all ways a bunch of used mower parts there.

The keyways position has to match the old one or the ignition timing will be off, and the altanator magnets as well, (so the charging will be right). Or the trigger magnets might match if the fly wheel is a bit different.


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## whitecloud20xx

you are right on the screw but it is a single magnet with a plate in the middle and the magnet is shaped like a C but squared off.


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## jrrdw

A "C" shape, do you mean like a horse shoe? If you can turn the magnet 180 degree's and see if it changes the cylinder that fires to the one that doesn't...


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