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Old 01-19-2015, 07:26 PM   #1
SocalMotoRider OP
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Need electrical help on a 1999 YZ400F

I just picked up a project bike hoping to get back on the saddle.

It's a 1999 Yamaha YZ400F and does not want to spark/fire so i downloaded the manual to check voltage etc. and here is what i found.

First i checked the obvious getting fuel,stop switch and spark which i am not sure but the spark is there but looks pretty faint but seems to jump across.

Next i broke out the meter to test the coil and CDI and here are my findings

CDI magneto inspection read 282 should be 248-372 GOOD

Source coil 1 resistance read 332 should be 720-1080 BAD

Source coil 2 resistance read 46 should be 44-66 GOOD (barely)

Secondary coil resistance read 11.57 should be 9.5-14.3 GOOD

Ignition coil jumps around ALL over the place and should be 0.20-0.30

Sooo hopefully some one has a better idea than me on my next step before i start throwing money around i don't have Haha Thanks in advance

Also bike does appear to have a aftermarket stator and i am guessing it's either a bad coil or stator ???
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Old 01-20-2015, 12:59 AM   #2
Beezer
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source coil is low ohms = shorted internally. the only time that might not count is if there were an aftermarket CDI that uses a different value coil


as for the ignition coil ohm reading... anything under about 10 ohms or so is a tricky read unless you have really good leads, and even if you have good leads, any reading under about 2 ohms is sketchy unless you have a lab quality meter. best you can hope for with "normal" equipment on a low ohm reading like that is... somewhere close, and not open, not shorted.

on a digital meter you have the percent of accuracy within the range.... then plus/minus at least one digit in the last decimal place. the leads themselves can have a couple ohms resistance. sometimes that varies depending on how you hold them
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if I'm answering your question, I assume all the obvious points have been addressed, such as " did you do a compression check?" and "is it still on fire?"

Beezer screwed with this post 01-20-2015 at 01:05 AM
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Old 01-20-2015, 08:44 AM   #3
SocalMotoRider OP
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Quote:
Originally Posted by Beezer View Post
source coil is low ohms = shorted internally. the only time that might not count is if there were an aftermarket CDI that uses a different value coil


as for the ignition coil ohm reading... anything under about 10 ohms or so is a tricky read unless you have really good leads, and even if you have good leads, any reading under about 2 ohms is sketchy unless you have a lab quality meter. best you can hope for with "normal" equipment on a low ohm reading like that is... somewhere close, and not open, not shorted.

on a digital meter you have the percent of accuracy within the range.... then plus/minus at least one digit in the last decimal place. the leads themselves can have a couple ohms resistance. sometimes that varies depending on how you hold them
Thanks for the info. so your saying it's a bad coil ?
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Old 01-20-2015, 12:52 PM   #4
Beezer
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yes.... from what your readings say, source coil 1 has an internal short. insulation in the windings has broken down and a connection is made between wires in the windings. that cuts out some of the windings & will reduce the signal it is supposed to generate
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if I'm answering your question, I assume all the obvious points have been addressed, such as " did you do a compression check?" and "is it still on fire?"
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Old 01-21-2015, 08:47 AM   #5
SocalMotoRider OP
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I appreciate the info. But am somewhat confused. It make sense about the coil having a internal short and the coil was my first thought as to what was bad however talking with a well known shop they are saying source 1 coil reading that low means a bad stator.

So do you think they are just saying that to get me to buy a more expensive part or is it possible ? Thanks again for your imput
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Old 01-21-2015, 11:46 PM   #6
Beezer
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I don't know the bike but there is a source coil, and a pickup or trigger coil (they have different names) that are only for the ignition system. sometimes these coils are separate pieces that can be removed, but they are often wound into the stator. if you look at the stator it will be apparent which style you have... if nothing unbolts the you have to replace the whole works
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if I'm answering your question, I assume all the obvious points have been addressed, such as " did you do a compression check?" and "is it still on fire?"
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