Hello all. I’m new to this forum. Anyways I have a Lawn Machine by MTD with a 15.5hp OHV Briggs and Stratton that won’t start. I had it to where it would start for a few seconds but then it would die. It turns over just fine and has a good spark. Carb is good. I took it off of another mower that works just fine. Battery is fully charged. I’ve done continuity test on all the wires and connections and everything checks out. Also has a new starter solenoid. Not sure where to go next. Please help lol. Thanks
GEt some carb cleaner.
Spay a SHORT shot down the plug hole & seel if the engine fires
If it does not then pull the blower housing and check the timing key in the flywheel.
#3
Richard320
Sounds like a timing issue to me. Like maybe the flywheel sheared the key.
GEt some carb cleaner.
Spay a SHORT shot down the plug hole & seel if the engine fires
If it does not then pull the blower housing and check the timing key in the flywheel.
is the magnet on the flywheel rusty at all? how bout the ignition module, rust or debis on it? also have you checked the air gap. saw where you said it had good spark but what did you test that with, sometimes grounding the plug is not suffitiant
Rust on the magnet makes absolutely no difference what so ever.
Some twerp who was asleep during science class at school made a video where they wire brushed it and from then on they all must be shinny clean
The only time rust becomes a problem is when it gets thick enough to bridge the gap between the magnet & the coil laminations which will work is heavily rusted as well , even to the point of the rust causing the laminations to spread.
i had a mantis tiller and it had spotting rust on flywheel. couldnt figure out what was going on with it. finally cleaned the rust spots off and it fired and ran as it should. i did notice that using my ohm meter i would loose conection when i went over the spots with rust. i read a forum one time where it talked about rust pulling power from the coil. not really trying to argue the point but the reason i asked him about it was simply because it hadnt been mentioned and far as i know it could be rusted like a junk yard rim. and if that was the case it could effect consistant spark
The only place rust is a problem is on a joint that should be an electrical path because all metal oxides are insulators, both thermal & electrical .
And as mentioned if the rust shorts out by bridging the gap.
SO the problem was highly unlikely to be rust.
If it was the coils would have some sort of rust proofing as would the magnets.
The reason they don't is because rust is not an issue.
Because the wrong information is so pervasive on the web it is prudient of those who know it is wrong to point that out whenever it is seen before it becomes an undisputable truth, commonly called Urban Myth.
NExt time you are in a big junkyard that uses a magnet grab to shift the steel around, walk over and have a loot at all of the rust on the magnet.
Bert, don’t you know that it is on the internet it has to be true. Right next to the Yeti, the government is here to help, and little green men from Mars. That being said, RUST HAS NO EFFECT ON THE MAGNETIC FLUX FLOW, UNLESS IT IS A NON-FERROMAGNETIC MATERIAL. Small engine magnets are a Ferris/iron material. A basic understanding of how a magneto ignition system works will show you how the interaction between a spinning magnet and the legs of a magneto work with a coil of wire to produce electricity.
#11
ILENGINE
Rust doesn't effect the magnetic flux between the flywheel and the ignition module, but it can effect the air gap which can effect spark.
And wire brushing a standard soft iron magnet with a power brush actually reduces the strength of the magnet.
Not a problem with the powder pressed rare earth magnets but you won't find them on a mower engine thats for sure.
I appreciate that rust can reduce the effecive gap and that would advance the timing by an amount so small it is impossible to measure with standard equipment and it there is enough rust it can bridge the air gap with the same effect as the legs rubbing on the magnet, which also destroys them, but iyhas to be h sort of rust you get from sea water exposure for many hours at an elevated temperature
