Fried my magneto coil...


New Member
Apr 24, 2014
Hi everyone.

I built my first gas bike and joined the site about 3 months ago - minimal problems so far, and people here have been very helpful.

Not really looking for help this time since I solved the problem myself and was able to cannibalize a working coil off one of my roommate's spare motors. Just wanted to say hi and relate my observations.

The old (working) coil I put in was grimy and oily, while there was nothing visibly wrong with mine (which was officially declared dead by a voltage meter) all the connections were solid. The first time I started her with the new (old) one, she started with such power and IMMEDIATELY started to hum. I cranked the throttle and she squealed!

What is notable about this was that prior to this, she took a bit more effort to start, and would perform sluggishly for the first block or so. I could rev the throttle to warm her up quicker, but if I did it too hard too soon she'd die.

And now she's performing better than ever, right off the driveway!

I guess it does make me curious though, does a condition like that cause performance/efficiency issues the whole time the bike is running, or just when it's 'warming up'? Was I wasting fuel before? It's a very noticeable difference in how it runs now; should I notice my tank taking me further?

I guess I'll find out over the next week but I'd love to hear any input!



Old, Fat, and still faster than you
Oct 8, 2011
memphis Tn
Sounds like classic weaker spark symptoms.
The new coil cleaned up your combustion and reduced four-stroking due to the spark being blown out or overpowered.
Might check the jetting. A stronger spark can change what the motor likes.