My 12-year-old Murray (Briggs 14.5 hp) riding mower 287707 has developed a starting problem. I tried to "cheap out" and buy an off-brand starter late last summer, it jammed the flywheel, whose teeth I then messed up unjamming it (!). I finally broke down and bought proper Briggs starter and flywheel plus new fuel filter, and have gotten the whole thing assembled. Now the starter cranks to beat the band but the engine will not kick in. I have checked the spark plug and I see a small blue flash across the arc of the plug. Why won't this engine start up? Never had an issue before I screwed up the starter/flywheel! Best way to check the carb? Any help most appreciated!

You have probably sheared the flywheel key due to improper torquing of the flywheel nut. Check the key, I think you will find the problem there.

Sorry for the dumb follow-up question: how do I tell if I've sheared the flywheel key? I'm not sure I know what the key actually is... or if I've sheared it.
My parts list for my engine doesn't list a separate key... looking at it now, I see I should have stated that I replaced the GEAR on the flywheel, not the entire flywheel.
Thanks!

I checked www.searspartsdirect.com and they list a key, but there's no picture of it.

So, let's take a different route:

http://www.freeengineinfo.com/sheared-keyway.htm

There is a slot in the crankshaft and a slot in the flywheel where a "key" is inserted. This "key" shears if the engine hits a rock or an immoveable object. Once it shears, the engine is no longer timed properly and it stops.

If the page doesn't help, I'll try again.

Hey thanks--now I remember the key! It was fine when I took the flywheel off and put it back together. I'll have to take the fan back off to see if I messed it up when reassembling. If in fact the flywheel key is still correctly positioned, any ideas on what I should check next?
Thanks!

Get some carb cleaner. No starting fluid. Spray some into the plug hole. If you get a putter, then you most likely have a fuel problem.

If the plug isn't wet after cranking, then you definitely have a fuel problem.

Remember:

Air (remove air cleaner)
Fuel (wet plug or sputters with carb cleaner in plug hole or air cleaner)
Spark (less intense out of the engine)

Are the first few things to check.