Triumph Repair: TR7 carb vaccum nipple, vacuum advance, manifold vacuum

Question
HI, I have a 1979 TR7 with dual ZS carbs (federal). The front carb has what appears to be a vaccum nipple located behind the throttle butterfly pointing downward.  What attaches to this nipple, or is it capped off?  Thanks, Don

Answer
Hi Don,

Check that it is a "Ported" vacuum, meaning it has no vacuum at idle and does have vacuum with the throttle slightly open. Then look at your distributor vacuum unit to see if it is a vacuum advance unit or a vacuum retard unit. Usually an easy way to tell is look at the vacuum diaphragm and note which way the vacuum port is pointed. If it is pointed toward the distributor is is a vacuum retard unit and if it is pointed away from the distributor it is a vacuum advance unit.

Vacuum retard units get straight intake manifold vacuum and if it is a vacuum advance unit it gets Ported vacuum.

The reason you need to look at it is because the original Opus/Lucas electronic ignition failed so often that they were replaced sometimes more then once while in warranty and many even switched distributors with other cars.

To add to your problems there was a port on the top of one of the carburetors on the flange which was also "Ported" vacuum but it went to the EGR valve if it still has one on it.

Howard