[T3] B brain

Jim Adney jadney at vwtype3.org
Sat Jun 9 23:23:23 PDT 2018

On 10 Jun 2018 at 0:31, Dave Hall wrote:

> Why would he only see a small spark? Doesn't that suggest a ignition problem?

I wondered about that, too, but it's really hard to know what to 
expect when looking at what a spark looks like out in the air. I 
remember being disappointed when I first did this test, many years 
ago. Since then, I've come to understand that the spark color depends 
on what's in the air, and the perceived intensity depends on your 
expectations and the gap.

For me, the only real test is to use a timing light with an inductive 
pickup. If that triggers, it means that something jumped the gap, and 
that's enough. It's binary, there's either a spark on no spark, 
there's nothing in between.

That's not to say that there can't be a difference between sparks 
produced by different systems, but with a given system, there's 
either a spark, or no spark. For example, I do a lot of repairs on 
Delta Mark 10 Capacitive Discharge Ignitions. With a flip of a switch 
on my tabletop test setup I can change from CDI to standard Kettering 
ignition. I can hear a difference, I can see a difference on an 
oscilloscope, I can even see a small difference in the spark, but 
when I'm testing, there's either a spark or no spark. I never get a 
"weak" spark that needs my attention to make it better.  

Well, maybe I should qualify that a bit: There are certainly times 
when some part is failing and we get a spark sometimes and no spark 
sometimes. That's what we call a "miss", and it can be difficult to 
track down the cause.

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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