How to troubleshoot CDI/Magneto when no spark

Hello all!

This is my first post. I picked up a used motor/bike at a sale this weekend (a King's Motor Bike Kit 80cc? I think), and it was in need of some serious TLC. However, for $15 I wasn't going to pass it up. I've mounted everything properly (which it wasn't before) and took it out for a spin. No spark.

I started at the beginning, taping my volt meter to the lines coming out of the magneto and went for a ride, and got a wide range of voltages (usually 3-4, only occasionally higher. I don't know if that is right. Seemed low, but I'm new to this engine. Additionally, the PO had lost the plug wire, so I bought a standard auto one and a like spark plug. Could my CDI be dead? Does anyone know a good way to check a CDI (ohms metering or something?).

Here's some pics of the new toy! Picasa Web Albums - cory - Chinese Motor...

Don't expect much in the way of voltmeter readings from the mag. What did you have the meter set on?

It does sound like you have a pulse. Good thing.

Take the plug out, so you can turn the engine over easy. Spin the rear wheel (in gear).....

So you get zero spark with a spark tester/grounded plug with a very small (.015") gap?

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Thanks for the follow up. Here's the answers:

I had the volt meter set in the 20V range. I was *mistakenly* thinking I was looking for 12V.

Let me adjust the gap when I get home and see. I didn't have a gap spec, but I couldn't get either the old or the new plug to spark. I am also not familiar with a spark tester. Would you suggest the easiest way is to just touch the side of the plug to an exposed part of the frame while cranking?

Can I put my meter on the output side of the CDI and expect to see anything? Do you know the Volt range I might see?

Thanks for the next steps. I hate when I want to troubleshoot but can't think where to go next.

Stupid question but I have to ask, are you sure you have no spark. Have you taken the plug out, laid it on the head and turned the engine over while looking for a spark.

Any reading coming out of the magneto would satisfy me. They have those cdi modules on ebay but I would be real sure that it isnt something else.

Does it sound like it is turning over when you drop the clutch. Some of the guys had clutch slipping so bad the engine wasn't turning when the clutch went out.

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Worse case I would think is you'd have to buy a new cdi and mag coil, both are under twenty dollars each.

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Excellent. I'm so glad you sent me back to double check. I'm used to a much higher voltage system, so I wasn't looking close enough. Turned out the light in my garage though, and there was consistent spark.

Now all I have to do is get the thing to start. I think it got pretty flooded, so I'm going to clean it out, and get some good, fresh gas in the tank. More updates pending...

Thanks again!

Welcome to the forum. Lots of motorize bicycle enthusiasts here. Wow, you got a bike with motor on it for 15 bux. Man, thats a steal. You'll like it here. Lots of helpful folks. Post some pics of your bike. We really like to see pics here......................

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Yeah that's the ticket. What plug brand and part #?

Mine has been in the same situation, to the point I had to take the head off, wipe the cylinder and head off, and reinstall, retorque, new plug and it fired right up.

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I'm getting 260-280ohms at the mag...I did get a reading of 300 one time, dont know what that was about....CDI/Black wire to plug lead 2.3 at 200K

$15!!?? NICE SCOORE!!Cheers

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Dan