Small Engines (Lawn Mowers, etc.): Tecumseh OHV17 engine, spark plug gap, inch gap

Question
I have a Murry 42" cut mower with a Tecumseh OVH17 204606B(H)  stp49ou1G2RP engine. Everything about the mower is in good shape except the motor won't crank. It will only pop. A back yard small engine man has it and has took the carb apart and put in a new spark plug. He said he put his spark tester on it and it looked yellow and the gap on the plug looked weak when cranked. He said it needs a new coil. I ordered one from Amazon.com last night. It is a Stens brand. Recently, a friend had a 14.5 briggs engine that would only pop and it was the timing key sheared. The man that is working on mine said he checked the timing key and it was fine. I have heard Tecumseh timing keys are made of steel. I don't know. Anyway, I would like an expert's opinion. What do you think could be the problem and what else is there to check? I also need a manual for this engine if you know where I can download one. From the numbers, can you also tell me the year of manufacture? Any help with these things will be appreciated greatly.

Stephen

Answer
The larger engines rarely shear flywheel keys.  However, if you saw spark odds are the coil is fine.  I have only found one coil that would jump the spark plug gap but would not produce enough spark to run.  I used an inline spark tester with a .166 inch gap to verify the defective coil...the bad one would not just the .166 gap that simulates the spark required for the engine to run.

I would start by checking the valves.

Check out the link below on how to check the valves:

http://www.smallenginesuppliers.com/html/engine-specs/tecumseh/Tecumseh_4-Cycle_

Eric