Triumph Repair: 1968 GT6, intake leaks, vacuum booster

Question
QUESTION: This car sat for about 4 years. It had run well in the past but no longer.  Some
prior owner put a pair of Stromberg 175 CD 2 carbs on it.  Last week I pulled
the carbs, replaced or cleaned everything that was worn or dirty and put
them back on the car.  It starts great, sounds smooth and seems to have
good power.  I can not get the idle rpm under  1200 or so.  The idle screws
on both carbs are all the way out.  Do you have a good suggestion as to
where to look next?

ANSWER: Hi Garry,
No engine can run at 1200 RPM without a lot of air, so look for a vacuum leak, unless your throttle butterflies are messed up. Don't forget the vacuum booster for the brakes.
Howard

---------- FOLLOW-UP ----------

QUESTION: Thanks, I am finding leaks and fixing them.  I do not find a vacuum booster
for the brakes.  

The car has an electronic ignition.  It was painted black by a prior owner so I
can not be sure but I think it is the Crane 700.  Does this device have any
adjustments that require attention?

Answer
Even though an advanced ignition timing can speed up an idle it is completely impossible to get 1200 RPM if the throttles are closed and there are no intake leaks. The intake system (carbs and intake manifold) controls the idle speed 100%.

If the throttles are completely closed and you have no intake leaks the engine can not even run let alone idle at 1200 RPM.

One trick to diagnose a vacuum leak is to remove the air filters and slowly restrict the amount of air allowed into the intake of each carb one at a time. If while you are closing off the air supply the engine RPM speeds up a little, you for sure have an intake leak (carb to manifold, manifold to head or vacuum hose)
If the engine never speeds up but continually slows down to shut down then you have a throttle plate not closing all the way.

I have no info on watermark ignitions systems but no brand of ignition can make a car run with the air shut off.

let me know,
Howard