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It's killing spark plugs. but why!?!?



ORIGINAL 1ST POST:

I'm trying to track down an intermittent spark issue originating from the stator....

as you can see in the pic below, i'm getting 1.7 ohms between the black ignition wire and the backing plate. The points are spaced open with cardboard. 

I couldn't find the actual spec anywhere in the manual, does 1.7 seem right for a cold reading? 

I know the condenser is also a possibility, so I have another condenser coming in shortly but I cant test the current one until its disconnected, so i'm trying the source coil first. 

Thanks! 

 

My electrical stuff is a bit of luck & guesswork. But i think to get a true reading you'd need to lift the condenser away from earth. The source doesn't have much resistance & i've never had much luck deciding if good or bad. If they total fail--open circuit--then its clear cut. At least with high resistance CDI source that's pretty conclusive if there's a 'big' difference between what it has & what it's supposed to be--when looking for spark. Is yours running ratty or not at all.

It's usually between 1 and 2 ohms with condenser in place like you have it...  I'd say your fine. 

Often points just need to be cleaned correctly...  what reading do you get with cardboard removed? 

It's not running at all. well...intermittently it will just not produce spark and not run. then it'll produce spark for a few kicks randomly. then nothing again.  

I've cleaned the points with sandpaper already.

with cardboard removed resistance is 0.0

I suppose at this point I'll de-solder the condenser and test it. I have a new condenser coming in on monday (along with points), in case that's the issue. 

The only thing you can tell about the source coil with an ohmmeter is whether it is directly shorted (zero ohms) or completely open (infinite resistance). 1-2 ohms means the wire is intact, but that's it. The wire has a very thin coating of insulation which can break down over time, allowing voltage to jump between windings. The coil normally produces 200-300 volts, but only for a few milliseconds, so this is difficult to measure unless you have a meter with a fast update time (1ms) or an oscilloscope. A megger or Hi-pot (special tools used to test motor windings) generates 500volts or so to check resistance and could tell if the insulation is breaking down. 
alnarv

Pulling strips of white card stock (strips of uncoated paper business card) through contacts until paper comes out clean is best practice in my experience...  even with brand new points.  On occasion, a little bit of grit, corrosion, or debris can stop the points from making consistent contact..

New points or ones that have been sitting around often have an invisible layer of corrosion on them...  using electrical contact cleaner before the card strips is helpful too.

In your case it more likely might be condenser.  Not sure. 

P.S. Even after sanding or filing "spotless"... even if contact cleaner used... you'll always get a black streaks on business card strips for a few passes.

#6 are you talking cdi source at 300 volts? not 6 volt points mag. I'm easily out of my depth but usualy get there in the end lol.

No, I am talking points/mag ignition. I did a set of pics of oscilloscope traces a while back, showing the output of a ct2 point system I had trouble with. After replacing the source coil, I unwound the old one to find the bad insulation area. It had about 85ft of copper wire, hence the 1-2 ohm resistance.