[T3] B brain

Jim Adney jadney at vwtype3.org
Sun Jun 10 18:37:34 PDT 2018


On 10 Jun 2018 at 19:06, Keith Park wrote:

> I remember coming into Winnemuccca NV, a slight miss for he past 100 miles
> turned into a cylinder down as we pulled in.  Turns out the spark plug
> connector resistor was burned out and as the gap to jump got bigger the
> spark at the plug got weaker until it wasnt there.

I remember that incident, too. Weren't we we stopped at a little 
Mexican restaurant? I recall a white wooden walk with roof and enough 
overhang to get ourselves out of the sun while troubleshooting.

This is a rather common problem with our ignition systems, but it is 
easily avoided by checking the resistance of each SP 
resistor/connector at every tuneup. They should each measure ~1000 
Ohms, but the exact number is unimportant. If you find one that has 
gone open (infinite resistance) it should be replaced. It takes a 
long time for an open resistor to start causing a spark problem, so 
if you replace the connectors when they first go open, they will 
never get bad enough to give you headaches.  

This is all leading us to the unspoken question that lurks behind 
this issue:

Q: Is it possible to have a spark that jumps across the SP gap but 
that's too weak to ignite the mixture?

A: No. If the mixture and compression are good, any spark that jumps 
across the SP gap will ignite it.

This is why I like timing lights with inductive pickups. They react 
only to current, and current only flows if a spark jumps the gap, or 
if the current finds another path to ground, which makes it possible 
to fool the inductive pickup.

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