For anyone who is familiar with magneto problems

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Thread Starter


Joined Dec 23, 2015
I have a Victa flat twin mower (170ccs) with a twin spark magneto coil, which I can only get to run if I disconnect the front cylinder spark plug lead, connect another plug to that lead and earth that plug. It will then start and run well but on the other cylinder only while the other plug sparks furiously on the base plate of the mower. If I rev it up very high and quickly Flik that plug out and re-connect the lead to the original other plug , it will continue to run, but If I miss the quick change over, re-connecting the lead causes it to stop. What is happening here? I hope someone can tell me.


Joined Sep 24, 2015
Your description is hard to follow. At least it is for me. Can you post pictures of what you mean? Sounds like you have two spark plugs. Does that mean yours is a two cylinder motor? [edit] Just re-read your post. OK, yes, two cylinders. [end edit]

A magneto is a pretty straight forward device. A magnet passes the core and generates a charge. That charge then breaks down and creates a big spark. There's more to it than just that, but that's the most basic rudimentary description I can give you. One magneto - one spark plug. At least that's my understanding of it. I'm sure someone has built other style magnetos's. Lots of small aircraft use magneto ignition, so I'm sure there's something out there I'm totally unfamiliar with.
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