[TR] Vacuum advance/retard

[Randall]

> The 68 TR250 & early 69 TR6 to my knowledge were the only 
> Triumph's to  have 
> both VR & VA.

Early Stags also had both, as did at least 69 GT6+.  The documentation I
have handy indicates that the 69 Spitfire Mk 3 also had the spark retarded
at idle, although it did not use a vacuum capsule to retard the spark.

>  I can attest to the total nightmarer trying to 
> tune  these as 
> originally designed with non adjustable ZS's too boot.

ISTR the TR250 was further complicated by using manifold vacuum for the
retard, with a vacuum switch operated by the throttle linkage to kill the
retard when the throttle was opened.  Likely a symptom of BL being caught
off-guard by the retard requirement, and not having time to get a suitable
vacuum port added to the carbs.

At any rate, my 71 Stag seemed to run pretty good with both VR & VA.  The
second Stag has a 73 motor in it with only the VR (which is disabled) ... my
plan is to eventually add VA to it as soon as I find a UK-spec advance
capsule at a reasonable price (Paddock's were sold out when I last checked).

Randall