Outdoor Power Equipment and Small Engines - Craftsman Lawn Tractor - B&S - won't start

Info I have:
About 10 years old
Sears Craftsman
Briggs and Stratton Engine
Model#: 944607041
Ser #: 021497E0010.67
14.5 HP
287707
Type 025501
Code 97020420

Symptoms:
When started, it cranks over, but doesn't start. It backfires. Have checked Spark Plugs, they are all fine.
Ideas?
Considering it may be Flywheel Key. Does anyone know if this model has an aluminum or zinc key?
Thanks all,
Courtenay Watson (who doesn't actually have a clue. My grandfather is telling me this information..)

Sounds like the timing key sheared. Timing keys are very cheap. Just take the broken pieces to your local hardware store and it will probably have these types of keys. (might not be labeled as TIMING keys) They cost around $1

Will grampa know how to get this timing key out? Can you send me a link or describe how it is done? Thanks,
Courtenay (Who can fix computers and train dogs but is hopeless with anything that uses gasoline)

First, if you do in fact have sheared flywheel key, do not pick one up at a hardware store. It likely will not be for the intended purpose of a small engine. Purchase the exact replacement (Briggs part number 222698S) from a local Briggs & Stratton dealer/shop, which is aluminum, by the way. Second, it is very unlikely (but not impossible, mind you) that you have sheared a flywheel key on a riding mower and since I cannot identify your machine, by way of the mower model you posted (on the Sears site), I don't know if this is a belt drive or a shaft drive unit. A shaft drive would increase the likelihood of a sheared key but still relatively improbable. I would be more inclined to believe that you have a faulty ignition coil, or, a kill circuit issue - even though you state that you have spark. But you indicate that you have more than one spark plug, which being a model 287707, Briggs, this should be a single cylinder engine and therefore have only one spark plug. How many spark plugs (cylinders) do you have? The best way to know if you have a faulty coil is to use an inline spark tester and be sure to isolate the ignition coil from the kill circuit by way of removing the kill wire AT the coil and then testing for spark.

Puey, whats wrong with keys from the hardware store? I always use those whenever I need one and they work fine. Seems like a little piece of metal is a little piece of metal wherever you get it.

If it's aluminum, and was made with the intention of being used specifically as a flywheel key for Briggs engines, then it's fine.

If it's not, it may not ever cause a problem, but then again, it could cause a big problem. It can even cause injury or death.

So we changed the flywheel key, and it still did the same thing (turned over, didn't sound like it was building compression, then BOOM backfired). A day later, now it won't do anything. We turn the key, and nothing. no click, no turn over, nothing. Ideas?

Sounds to me like it has a stuck valve, or one that is too tight at least.

How is this diagnosed/treated?

The fact you have no noise with the key now is the first item you need to tackle though. Perhaps you have worn down the battery from all the attempts at starting to the point of an extremely low voltage situation. Place the battery on charge sufficiently to bring it back up to snuff and then you can diagnose the starting issue. Remove the rocker cover to have a look at the valve train looking for proper placement of the push rods first. Be sure to remove the spark plug so that you have no resistance when performing the checkup. Then, using a knitting needle or similar blunt, long instrument, place such in the spark plug hole making sure to contact the top of the piston and then rotate the flywheel by hand and get the piston positioned at 1/4" past top dead center (TDC) on the power stroke. To obtain this position, rotating the flywheel in a normal, clockwise rotation watch for the intake valve to open then close, the knitting needle will then be on a outward movement and bring the needle to the top of that stroke and watch for the needle to begin an inward movement and allow it to drop down 1/4". Both valves, now, are assured to be closed fully (in theory and if all is well with the valve train, that is). You can now check the valve clearances between the valve stem and rocker arm on each valve, setting both at .005". Once this is accomplished you now want to make two full revolutions of the flywheel (for each complete cycle of your 4-stroke cycle engine) and watch for proper operation of the valve train as well as the operation of the MCR (mechanical compression release) whereas the lowest valve in the cylinder opens slightly (about .004" on the compression stroke) watching for any binding of either valve during their respective cycle. Do this and report back with any issues out of normal or questionable.