[T3] B brain

[Jim Adney]

On 10 Jun 2018 at 6:06, donrob at yachtsales.com wrote:

> I have seen a bad coil produce as very weak spark (especially in small one
> cylinder engines) where the engine would run, but not well.  A new coil
> fixed it right up.
> 
> I once had a beetle come in with an odd looking coil that didn't run
> right.  Replaced it with the correct Bosch unit and it ran properly.

Yes, I've seen problems like that, too. Those are difficult to quantify and 
seem more like an extreme miss than simply a weak spark. It's quite possible 
to get spark when the situation at the gap is easy, so the spark can jump the 
gap, but when the cylinder pressure is high, and higher pressure makes for 
better insulation, the voltage can't get high enough to jump the gap.

This makes for a sort of "situational miss" where an engine may idle, albeit 
poorly, but die completely when the throttle is opened.

It's certainly true that if I see a poorly running engine with a bunch of odd 
aftermarket parts replacing the reliable Bosch OE parts, the aftermarket 
parts get my first attention.

We also had a list member a few years ago who had been sold the taller 
Beetle dist cap for his Type 3. That meant the spark had to jump a couple 
rather large gaps inside the distributor in addition to the gap in the spark 
plug. Since the Beetle cap is maybe 1/2" taller than our cap, it amazed me 
that the engine ran at all. I don't remember the details, but I don't think it was 
driveable.


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