craftsman lt 4000 problems

I have a craftsman 4.5 HP mower model 917388630 that has Tecumseh engine model 143044500. The motor has no fire. I changed the spark plug and also the coil and still no fire. What else would cause this problem?? Thanks for your help

Troy Bilt Model 860, High Wheel Rear Wheel Self Propelled, Briggs and straton engine, alright this is really buggin me to get workin with grass starting to show up, but last year hit a stump hard enough to shut mower off, since then mower would puff as it run, lost the first pull start after that, sometimes 2 or 3 good hard long pulls, so by the end of last year it wouldn't start at all no matter how many pulls. Since last week i have taken off valave cover and noticed that the gasket has tore so i have one on order, and i had no spark, cleaned the armature (badly rusted) with sandpaper set to .010 gap and put all back together, now when i pull i get a loud backfire and sometimes a shot of fire outta the exhaust, but still wont run. So im tryin to figure what part to by to fix and/or should i just buy a new one. The mower is 2 years old but for the first year I did some weekend lawn jobs. I just am really impressed with this mower and would recoment to anyone and want to fix it, myself