Small Engines (Lawn Mowers, etc.): Snapper tiller prob, dremel rotary tool, rear tine tiller

Question
Good morning,

Hoping you can help.  I have a Snapper rear-tine tiller with a Tecumseh engine on it (approx 7-8 years old).  The tiller was in storage for a few years and I recently brought it back out.  It's had a tune up including new plug, oil, & air filter.  Starts up like a dream.  But.....

I was using it a few weeks ago in my yard and it ran great for about 15 minutes or so.  Then all of a sudden it shut down and was difficult to restart.  When it DID start up, it only lasted about a minute and then shut down again.

So far here are the diagnostic checks I've done: breather, plug (even though it's brand new), and fuel cap.  Advice I've gotten from a local shop: they said if it ran for 15 minutes, then it can not be a carb problem.  They claimed the magneto may have been rusted over and (as a result) when it gets hot, it's no longer functions properly (until it cools down again).  So I located the magneto and they were correct with the rust part.  I cleaned the rust off the magneto with a spinning wire brush (looks brand new ), and did the best I could with the magents on the flywheel with a dremel rotary tool (they don't look AS clean, but still better than before).

Upon putting everything back together (fyi - I have no engine manual - just going by eye), I start it up (again - starts great), but NOW it shuts down after a minute!  It ran better BEFORE I cleaned the rust off.  Now it runs worse.

Do you have any suggestions on what might be wrong?  Did I possibly place the magneto back on wrong or is there a certain gap requirement between the magneto and flywheel?  Did I possibly ruin the magnet's polarity by using the dremel rotary tool?  If this isn't the problem, are there any other diagnostic checks I can do?  It's such a small engine and I can't imagine it being THAT difficult.

Thanks for any tips or advice you can give me.

Joe

Answer
Hi Joe,

I'm not convinced that it is a spark problem until you test for spark.  When it quits, check it at the spark plug, to confirm.  There is a gap required at the magneto but I'm not sure what it is.  If you have spark now, I don't think the gap is the problem.  If you have spark when it quits, try adding fuel to the carb intake to test for a lack of fuel, which is the usual peoblem with engines not running.

Let me know what you find.
Michael