[T3] On a 73 T-3 SB fuel injected aut trans pinging .

[Jim Adney]

On 5 Dec 2017 at 18:44, William J wrote:

> The Bently state to set the timing to have the lines off and plugged and 
> only states the engine RPM at 850 idle . Is this correct? And if so when you
> raise it back to 950 plus or - 50 RPM this may advance the timing a bit. for an
> auto matic car.  What is the best way?

It's always a problem if the distributor is already started up the 
advance curve at idle. This leads to the vicious cycle I mentioned 
earlier. You might want to try lowering the idle speed slowly while 
watching the timing to see where the advance starts. For the AT AH, 
it should start somewhere above 1000 rpm. So timing at 950 should be 
fine. Note that since there's no advance between 850 and 950 for the 
AT AH distributor, either speed should give you the same correct 
result.

But, if you find that your advance is starting below 1000 rpm, you 
might try swapping the springs, just in case they got swapped before. 
If that doesn't fix it, you're looking for someone with a distributor 
machine.

As for the springs, one will be snug when stationary and that one 
will hold the advance to zero until its preload is met, then it 
controls the early, low rpm, advance.

The other spring has an elongated loop so it doesn't come into play 
until some higher rpm, then it stops the advance until the 
centrifugal force also overcomes that spring's preload; that gives 
the flat section of the advance curve.   

Once the second spring's preload is met, the advance continues, but 
now the advance curve is less steep, because the centrifugal force is 
working against the combined strength of both springs. 

One other thing to check is to look at the 2 arms that got adjusted 
at the factory to set the advance curve. Look for any signs of 
damage, because sometimes someone loses the screw that holds the 
little plate that holds the points connector to the outside of the 
distributor. If they replace that screw with something longer, it can 
reach in and bend those arms when the distributor turns. That 
completely destroys the advance curve calibration.

Hint: Any time you've done distributor work, always spin the 
distributor shaft by hand before reinstalling it. If there's an 
interference problem, it's MUCH better to discover it by hand, before 
you let the engine force it around.

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