Small Engine Problems? Ask an Engine Mechanic for Answers ASAP
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Can you tell me what 2-diode harness you used and what manual said to do this? I'm a bit confused by that statement, since usually the diode is on the charging coil (to convert AC to DC for battery charging), not the ignition coil.
This sounds more like a grounding problem to me. There is a small ground wire that is connected to the base of the ignition module that has the purpose of grounding the coil and stopping the spark to kill the engine. If this wire is improperly grounded through damaged insulation, or any other contact to ground it will prevent spark from occuring.
Can you give me a bit more info please?
Thanks for your help. This 2 cylinder engine has a magneto ignition system with two coils (armatures), one for each cylinder. On page 58 of the BS Vanguard V-Twin OHV Repair Manual (No.272133-6/04), the two diodes are shown in the wiring diagram with one for each coil. The ignition armatures are electrically separated by two diodes installed in the wire harness that connects the ignition armatures to a single ignition switch. Information from a BS textbook (No. 2487 089484), page 200 states the diodes provide the independent ignition armatures a common path to ground so the engine can be killed with one kill switch to ground the primary circuit thus eliminating the spark to the engine. Without diodes each primary circuit of each coil would have a path to ground through the opposite coil. Our problem may not be in the diodes but may be something as simple as a ground, however, I believe we have a common probem with each engine since both have the same problem and the BS textbook as well as the repair manual indicates the problem is with the diodes. As I stated previously, we have ordered new diodes (come as two in a litttle wiring harness) and haven't received them. UTM is in a small town in NW Tennessee, i.e. out in the boondocks. We don't know if this will fix the problem. If it does, we hope to avoid a repeat, hence my reason for my inquiry to you. RS
Thank you. Now I understand. Have you tested for spark on each cylinder by completely disconnecting the the ground wire from each coil? That would eliminate the diode and ground wire and determine whether the problem was internal or external to the coil.
Also have you checked the diodes with a meter? Reading resistance you should have continuity in one direction, but no continuity if the leads are reversed.
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If you have a fuel shut-off solenoid on the carburetor, turning the ignition switch to the off position will starve it for fuel, so it sounds like that's exactly what is happening here. That will "kill" the engine as well as grounding out the ignition.
From your description of testing, it looks like you have certainly proven both ignition modules are good. The diode harness should resolve the shut-off issue based upon your findings.
Here's a rather generic diagram showing how those systems operate. Yours may be slightly different depending on the specific application.
I'm also posting a link to the book this diagram is taken from. There may be information in there you can use:
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