Small Engines (Lawn Mowers, etc.): Tecumseh engine wont start, stuart gap, compression stroke

Question
Craftsman Mower- model no. 917.374821 serial no. 052 404M 001705
Tecumseh Engine- model no. 143.046702 DOM: 04142CE0236
Engine Family: 4TPX8 1951BC
My lawnmower engine had been running fine, but then it stopped of its own accord. I had finished mowing so I thought it had just run out of gas.  The next time I tried to start it after refilling the fuel tank, it wouldn't start. I went through a series of checks and determined there was no spark. I then replaced the magneto and I am now getting a spark. The engine still shows no signs of wanting to start however. (There is fuel in the combustion chamber after priming the carb). The spark seems reasonably strong, but I don't know what the magneto gap should be, so I just set it by eye. Do you know what the gap should be set to, and do you have an idea what could still be causing the starting problem?
Thanks for any information.

Answer
Hello Stuart:

Gap the Coil at.020in. Tecumseh Says .010in, but I have Found this to be Too Close on Some Engines and the .020 has Worked Fine for for Me for More than 20 Years. Check the Flywheel Key. If the Key is Damaged, the Plug will Fire, Just at the Wrong Time in Relation to the Position of the Piston on Compression Stroke. Go to this Site Addy, http://www3.sears.com/ and Enter the Model Numbers in the Upper Left Search Box and Click Go. Then Visually Verify the Equipment and CLick Continue. From this Page you can View Diagrams or Parts Lists for you Equipment. Hope this Helps. I am here if you Require more Assistance. Let me know what Happens, Please. Thanks.

Good Luck

Respectfully

John