Small Engines (Lawn Mowers, etc.): snowblower, friction wheel, set screw

Question
Hi Michael, back in April I had asked you the question ""my SNOW FLITE MTD 8/26" snowblower, fitted with electric starter, cuts out after running for about 15 minutes and won't restart for awhile. what could be the problem? it has a tecumseh engine"; You had replied "to check for sparks  & for lack of fuel". I did so today...( since 2 feet of snow landed on us overnight)  and indeed there is no sparks at the plug after the engine cuts out but yet it restart OK 20 minutes later...would just replacing the plug fix the problem or sometning else is causing the problem?
Now my other snowblower has a traction problem, the spocket mounted on the hex shaft 'slips' and therefore does not turn the drive chain. is there a setscrew that keeps the sprocket securely fastened to the hex shaft? there is a ring retainer on the hex shaft about half an inch from the sprocket but I'm not sure what purpose it serves. the friction wheel looks all good and make A1 contact with the drive plate. many thanks  

Answer
Hi Marty,

If you have a good ground connection when testing for spark and are sure that there is no spark, then I suspect a bad ignition coil.  Changing the spark plug will not help.  

On the other snowblower, I think the sprocket originally had a hex inside the bore.  It may have worn smooth, requiring replacement of the sprocket.  A set screw probably would not hold up.

Let me know how you make out.
Michael