testing a magneto?

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matthurd

New Member
Dec 13, 2010
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manchester NH
2 weeks ago i was having no spark, got around to ordering some parts, ordered a new cdi because a few people here said they go more often then magnetos, anyways it didn't fix the problem so i opened the magneto panel and apparently some water and road salt had gotten in there and i'm guessing it's fried now. not sure how it got in it wasn't a very wet day the one time i rode it, and i had never opened that panel before today so the gasket should have been safe and solid.

anyways before i go and order another part that i actually don't need (although i'm pretty sure i do) i'd like to test it. new cdi new spark plug and no spark.

any ideas how to test it? my dads a former electrician so he has a few good meters if those are needed.

and how can i prevent anything from getting into that compartment in the future.

searching magneto testing didn't work very well for me so figured i'd ask, thanks.

guessing this is dead right?


 
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earl.k

earl.k

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Jan 19, 2011
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PA! USA
i read some place. that the small wire shown below in the pic. can sometimes go bad or come broke..



this could be your problem.. also do you have your kill switch hooked up.. because if it is grounded wrong. this will also cause it not to spark.. i have grounded mine wrong and know its a easy fix.. never hade a bad magneto, but if it is that wire im betting you could just mend it easily. or buy a new magneto.. good luck:) and here is another pic of a working magneto.





http://motorbicycling.com/members/earl-k/
 
2door

2door

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Staff member
Sep 15, 2008
16,302
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Littleton, Colorado
If you have an ohm meter, your dad will know how to use it, try this:

Use Low Ohm-Meter Scale About 200 Ohms

Magneto Coil

1) Check Ohms between BLACK wire and WHITE wire. Reading should be around 2 Ohms
2) Check ohms between BLUE wire and WHITE wire. Should be around 300-400 ohms.

CDI

Use Ohm Meter High Scale About 200-K
1) Positive lead on BLUE wire and Negative lead on BLACK wire should read infinite (no activity)
2) Positive lead on BLACK wire and Negative lead on BLUE wire. Should be about 130-150 K-ohms
3) Positive lead on Spark Plug wire and negative lead on BLUE wire. Should read between 135-155 K-ohms

Switch to Low Scale 20K
4) Measure between Spark Plug wire and Black lead. Should be about 2.5 - 2.7 K- ohms

As for keeping water/dirt out. Make sure the gasket is good or seal it with a small bead of silicone and fill the hole where the wires exit the case with the same silicone sealer.

Tom
 
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matthurd

New Member
Dec 13, 2010
817
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manchester NH
@earl the little wire and all other solder connections appear to be solid

@taco yeah the gasket basically crumbled in my hand

@2door ordered a new gasket from pirate as well as a new magneto but i guess testing to learn is never a bad thing, if it works i just have an extra and i need the gasket anyways, and do i need to be rolling the bike while he tests this or is this supposed to be done while stationary?

@adam it doesn't smell burnt, kill switch start is a no go although honestly i never had it working right in the first place this didn't stop me from starting it originally though, i did have it working originally.
 
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matthurd

New Member
Dec 13, 2010
817
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manchester NH
he metered everything out and he said everything checked out to be about right except the blue+white.


2) Check ohms between BLUE wire and WHITE wire. Should be around 300-400 ohms. he said this part was 300k ohms, not sure if its a typo or a misunderstanding? but other then that 1 connection he said we were in the right area.
 
2door

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
Mat,
the ohm readings should be taken with all wires disconnected. No need to roll the bike or rotate the crankshaft. Just read the meter with the connections as stated above.
After you have confirmed everything is as its supposed to be connect the wires as per the wiring diagram below. Do not rely on those little brass plug in connectors that come with the kit. Our best recommendation is to make the splices with a soldered connection then protect them with heat shrink tubing. As was stated by another member, make sure that white wire cannot come in contact with any metal component of the bike frame or engine.

Tom
 

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matthurd

New Member
Dec 13, 2010
817
2
0
manchester NH
2door said:
Mat,
the ohm readings should be taken with all wires disconnected. No need to roll the bike or rotate the crankshaft. Just read the meter with the connections as stated above.
After you have confirmed everything is as its supposed to be connect the wires as per the wiring diagram below. Do not rely on those little brass plug in connectors that come with the kit. Our best recommendation is to make the splices with a soldered connection then protect them with heat shrink tubing. As was stated by another member, make sure that white wire cannot come in contact with any metal component of the bike frame or engine.

Tom
Click to expand...
between you here and taco on msn giving us information we've found that the white wire has continuity (i think this is how it's worded?) which is a bad thing and means my magneto is shorted according to taco, luckily i ordered one from pirate along with a new gasket from pirate about 2 hours ago, with luck it will be here on saturday if he got it shipped today. so hopefully i'll be good to go buy monday, which i also expect my new sprocket adapter to be in either tomorrow or saturday so i guess the timings going to be decent (although unbearable if the weathers any good on sunday).

thanks for all the help everyone,appreciate it. :)

and when i get a new one i guess i'll sharpen up my soldering skills.
 
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txlixard469

txlixard469

New Member
Feb 21, 2011
72
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austin
i have oil in my magneto casing i kno this aint supose to be there but dont kno how it got there is a gasket or what busted
 
txlixard469

txlixard469

New Member
Feb 21, 2011
72
1
0
austin
and if you look at my album you can get a better idea im showing how it looks and i will look into gettin a crank seal can i get one at a store like a lawnmower store or something
 
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