[T3] odd issue RPM hangs.

[Jim Adney]

On 14 Oct 2019 at 11:57, William Jahn wrote:

> Jim , on the mechanical advance how did you come up with 21 degrees total.
> I only have the Bentley yet it shows 6 degrees yet this is dist speed on a
> machine so you double dist speed . I see the 72 dist chart dist installed
> and it's near 21 degrees and has no graph . This means to me you can't
> double the RPM and come up with 12 degrees. Or do you have another source
> you get the full advance or is this what you have checked with a light and
> recorded? I assume total being control in degrees dist shaft begins when
> the advance first kinks in at RPM  not from the set 5 * BTDC or are you
> just talking about 21 degrees is as far as the mechanical advance should
> reach?:

Looking at the Bentley recently, I just noticed for the first time that all the 
graphs are in distributor degrees while the charts for '72s are in crankshaft 
degrees. Bentley doesn't specify, but that's the only way these make any 
sense.

The 6 degrees you mention for '73 is the vac adv, averaging closer to 5 deg. 
The middle of the mech adv is ~10.5, which I doubled to get 21 crankshaft 
degrees of mech advance.  

To get the actual firing timing, you have to add the 5 crankshaft degrees 
BTDC at idle, plus any vac advance that comes into play. What this works 
out to is a max 26 deg of crankshaft advance under med or full load or 31 
deg under light load (cruising) when the vac advance kicks in.

The FI vac advance only comes into play under med or high rpm and light 
load. We don't get any vac advance at idle or when accelerating or during 
hill climbing. It's only while the engine is "loafing" at highway speeds. That 
improves fuel economy on trips.

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