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Triumph TR6 - Vacuum line ?s

I'm working on a friends '72 TR6 and I noticed that the upper radiator hose, runs into a section of pipe that appears to be a vacuum junction of some sort. It has 3 ports. One going the rear carb(looks to be the manifold side), one going to the distributor, and a 3rd that doesn't have anything hooked up to it. I also believed they are each labled with letters, (D, O, and don't remember the third, maybe M).
So I'm want to know if I need to cap the third port, or is there something it needs to be hooked up to?
Also, why did they attach it to the top radiator hose?
-Bill
Bill Mertz

This was part of the emission controls. It would retard the spark timing when the engine was cold to control startup emmisions. Plugging the port on the carb and removing the lines from the distributor retard(right side) is a popular modification. If you are subject to the sniff test, make sure the car is good and warm before submitting.

Don
Don Ho

But what is the 3rd port for?
Bill Mertz

Guessing here . . . the very early TR's had both advance & retard capsules on the distributor. Perhaps the mystery 3rd port is the advance vacuum source?

Rick O.
72 TR6
Rick Orthen

Rick,
just out of curiousity, does your '72 have these fittings. The best way I can describe it is: between the two sections of upper radiator hose, there is a metal pipe that joins thte hose, off of this pipe, there is a little manifold, where the carb vacuum line goes in to one port, the dizzy vacuum line plugs in to a second port, and the third empty port has nothing connected.
Bill Mertz

Bill,
I used to have a '72 with the thermostatic vacuum valve you describe and I remember it had an unused third port as well. I think there was one marked "D" for distributor and "C" for carb. The third one must have been for some other car.

Jeff
'74 CF13816U
JB Fetner

The thermo switch was intended to increase idle speed if the car started to get too hot. it does this by relieving the vacuum to the distributor at a certain temperature thus eliminating vacuum retard and increasing idle speed. I believe one port is always left open to relieve the vacuum from the switch to the retard capsule. This is based on the limited detailed references to this valve in the owner and service manuals and my car which still has all of its emission controls.

On my '74, there are 4 ports, two from the carbs (1 port on the switch receives vacuum from 1 port at the throttle plate on the top of each carb and another port on the switch receives vacuum from a port at the throttle plate on the bottom of the front carb) one to the dist and one vent.

What's interesting is that various manuals and diagrams show slightly different plumbing for the later 4 port valves....all part of what makes these cars fun.
wayne

Thanks Wayne and Jeff.
I'm thinking about just plugging the vacuum port on the manifold and disconnecting the vacuum from the retard unit on the dizzy, and setting the timing to around 4-8 degrees BTDC. Doesn't seem like I really need the retard unit as there is no emission requirements on the car now.
Bill Mertz

This thread was discussed between 17/05/2006 and 22/05/2006

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