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Motorized Bicycle Trouble Shooting Use this area to post problems that may arise, if you could use some help in figuring out what is wrong with your engine and what needs to be done to achieve top performance.

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  #1  
Old 10-24-2016, 06:24 PM
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THowell1975 THowell1975 is offline
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Unhappy Magneto coil keeps burning out

I have searched this forum and haven't found an answer for this one. I have a problem with my magneto. It keeps burning out. The wires coming out the side of the plastic and are soldered to the base burn up. I've tried to resolder them and they may work for a couple of miles and then burn up again right at the solder joint. I've added enough solder on top of that and tried again and it ran, but burnt up again and now there's no more wire left to resolder. I've burnt up three of these the same way, so I don't think the problem really is the magneto anymore. It's like I'm getting too much voltage for the wire or something. Could this be the CDI? Any way to check?

I also bought one more magneto that doesn't have the white wire at all, just the blue and the black (and no pesky wires soldered to the base) and it worked for a few days and then it quit. It actually ohms out good between blue and black, but it won't make any spark anymore. I tried one of my "resoldered" ones after that one and it worked for a couple miles until that little wire burned up again and I couldn't resolder it anymore. I'm completely lost and out of magnetos and don't want to order any more until I figure out this issue. Any help would be appreciated. Thanks!

Oh yeah, on the ones with the white wire, it is cut off and heat shrinked, so no way is that shorting anything out. I'm thinking that if it fires up and works, everything is good in the circuit. But if it burns out after just a few miles, there must be something else. Or are these cheap little magneto coils THAT cheap that I need to keep a half dozen spares at all times?? My spark plug is the factory one and I assume it's good. Every time I add a new coil, I get good spark again. Until the coil burns up...
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  #2  
Old 10-24-2016, 07:11 PM
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Agreen Agreen is offline
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Default Re: Magneto coil keeps burning out

Well, the input impedance on the cdi should (in theory) be pretty high. I would probably need to see a schematic before making that call. Anyway, check the resistance of the cdi, but it may not really tell you much. I'd try a new cdi and magneto.

How is your kill switch wired?

Can I also see a picture of how your solder job looks?

And no, the magnetos don't burn up that fast normally.
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Old 10-24-2016, 08:26 PM
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THowell1975 THowell1975 is offline
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Default Re: Magneto coil keeps burning out

Well, I don't have any pictures of my solder work, but I'll promise you it ain't very pretty. I've resoldered each one 2-3 times. They worked, so I assume I did a good enough job. The kill switch was taken out of the equation a long time ago, so that's not an issue.
I forgot to mention, I did try a new CDI and spark plug already. Maybe i should try all three at once?
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Old 10-24-2016, 08:46 PM
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Venice Motor Bikes Venice Motor Bikes is offline
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Default Re: Magneto coil keeps burning out

Yes, try all three at once & don't zip tie the blue & black wires too tight to the frame... just to be sure that doesn't cause a slight short.
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  #5  
Old 10-25-2016, 11:39 AM
crassius crassius is offline
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Default Re: Magneto coil keeps burning out

have you pried up on that end of crank with a screwdriver? your main bearing may have gone bad and it is shaking the coil apart internally
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Old 10-25-2016, 06:08 PM
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THowell1975 THowell1975 is offline
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Default Re: Magneto coil keeps burning out

Quote:
Originally Posted by crassius View Post
have you pried up on that end of crank with a screwdriver? your main bearing may have gone bad and it is shaking the coil apart internally
Yes, the bearings seemed good and crank seems solid. It's a fairly new engine with less than a 300 miles on it.
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Old 10-25-2016, 06:32 PM
crassius crassius is offline
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Default Re: Magneto coil keeps burning out

your problem seems more than can be solved without experienced eyes on the scene - last thing I can think of is exhaust pipe dumping a lot of heat right there thru a crack or hole
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Old 10-25-2016, 09:05 PM
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Agreen Agreen is offline
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Default Re: Magneto coil keeps burning out

Hmm... found some more information

http://motorbicycling.com/showpost.p...7&postcount=13

So how much more water gets in the cover when it runs for only 2 miles?

Like Crassius said, it needs some experienced eyes. Pictures help. A LOT!

Just trying to help you man.
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  #9  
Old 10-29-2016, 08:26 PM
Seabass Seabass is offline
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Default Re: Magneto coil keeps burning out

I think id check the magneto clearance first. It should be .010 or about a business card thick. I'm wondering if the cdi is not getting enough volts due to this and as a result it is drawing more to achieve saturation in the primary winding of the cdi. Remember the same current goes thru the ground as the positive. I think the soldered joint is just the weak link. Maybe you could install an inline fuse holder on the hot wire to the cdi and keep putting in bigger and bigger fuses till it stops blowing them. Id start with 1 amp.

I don't know but I'm sure I'd figure it with it in front of me.

Not to set mągnito clearance, rotate crank till magnet is pointed at mągnito. Slip business card between crank and mągnito. Loosen mounts to mągnito. Magnet will suck mągnito to business card. Tighten mounts.

Well at least that's how its done on Briggs, Tecumseh, Robin, etc....

Look at how my computer is spelling mągnito!!! I'm becoming my french canadianalter ego of myself...lol
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  #10  
Old 10-29-2016, 08:58 PM
Seabass Seabass is offline
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Default Re: Magneto coil keeps burning out

I think you should check the magnet to magnito clearance. It should be .010 or about 1 business card. The thinking is that the cdi primary winding is not achieving saturation due to low voltage and as a result is drawing more amperage . The melting of the solder is just the breaking of the weak spot. You could check this amperage idea buy installing an inline fuse on one of the cdi primary wires. I start with a 1 amp fuse and keep increasing it untill it stops blowing. You know the Chinese make crap so it would not surprise me if the gap was set way off. Hopefully it is adjustable. Been a few years since i had a China girl open. Good luck I'll be watching this thread.

Wow this is interesting. I'm probably about a mile off. I understand the cdi is not a coil pack but at the same time there is capacitance to it. Just put your meter on farad's and go across the primary wires

I'm way over thinking this one I bet..haha I think I need a beer to dumb it down

Last edited by Seabass; 10-29-2016 at 10:09 PM.
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