I've got a B&S 12.5 riding mower that absolutely will not fire up! This thing will spin like there's no tommrow but won't fire for anything! We've looked at the plug and it's fine.Battery is good or it wouldn't spin like it does.The serpintine belt was off so we put it back on and it seems to be good.Oil is clean and at normal level.It just will not fire. Has anybody got any clue as to what this is? Any help would be greatly appericated cause I'm ready to send this thing the way of Ol' Yeller.

Maybe check your valve clearence,and compression.
That's the best I can do with no model #