Small Engines (Lawn Mowers, etc.): Tecumseh OH140 intermittant ignition, electronic ignitions, safety interlocks

Question
Sometimes I have spark, sometimes not, and it is unrelated to engine being hot or cold. The switch tests okay, but I took it out of the circuit anyway and put a jumpwire across the connector in place of the switch. I removed the plug boot at installed a new terminal, well-connected to the lead. The gap between the taller magnet and the pickup is about .007". I have yet to make a flywheel puller so I can have a look at the alternator and ignition charging windings. However, the books say to check resistance from the wire (that comes from behind to the flywheel and connects to the ignition module)to ground. The desired figure is 400 ohms, and I'm reading 200. But when I do get spark, the engine runs fine and seems to keep the battery charged. I should tell you that this is someone's re-engine of a 35 year old Sears garden tractor that had a smaller Tecumseh flathead, so it has none of the modern safety interlocks that disable the ignition, so far as I know.

What thows me is the intermittant nature of the failure and its non-relation to heat. In my experience, electronic ignitions usually either work or not, unless they break down under heat. I expected to find a bad wire or connection, but have not yet spotted any.

Can you tell me if the alternator and charging winding for the ignition capacitor are the same between the OH140, OH160, and OH180 engines? will they fit under my flywheel? I know there is a 10A and a 20A alternator stator; do they take their own regulators, and will either one fit under my flywheel? (Obviously I'd rather find a serviceable used part than an expensive new one). Thanks in advance for your kind attention.

Answer
Hello Phil:

>>You are Correct; the Most Common Cause for Ign Module Failure is Heat.
>>However, it is Not Unusual for an Ign Module to Cause Intermittent Problems and it Not be Related to Heat.
>>The Charging Coil/Stator is the Same Part Number for the OHV140 and OHV160 Engines, but is Different for the OHV180 Engine.
>>You can Use the Site Addys at this Site Addy; http://www.yetmans.mb.ca/antiques.html to Search and Locate New/Used Parts or for Manuals for this Unit.
>>If you Hit a Snag or this Does Not Correct the Problem,  I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Be Safe and Happy. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Comments and Ratings are Greatly Appreciated. Thanks.

Respectfully

John