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TR6 Vacuum Lines

Gerry M

Its a 1974 TR6. The car idles fine and cruises smooth but hesitates under acceleration. I just noticed that the vacuum retard line from my distributor is not attached to anything. Could my acceleration hesitation be a vacuum issue?

I have attached photos of my current vacuum line setup. Vacuum 1 photo shows unused unplugged port on bottom of front carb. Vacuum 2 photo shows loose unconnected end of vacuum line coming from vacuum retard unit on distributor. Vacuum 3 photo shows line from upper rad hose temp sensor connected to port on top front of the rear carb and line from engine breather connected to port on top center of the rear carb. What lines should/need to be connected to what ports?



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  • Vacuum 2.jpg
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  • Vacuum 3.jpg
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You need to plug that fitting on the bottom of the carb where the retard attached and, according to your pic, has the rubber elbow attached to it. No need to plug the dizzy or the vacuum line attached to it. (Tip of the hat to Poolboy)


Country flag
Thank you arcom
Yeah, the 74 plumbing was a little complex. The nipple on the bottom of the front carb did supply vacuum to the distributor retard module, but on a 74, it was also the source of vacuum that activated the Throttle Bypass Valves...All that was done in the manifold that was attached to a fitting in the radiator top hose that housed the Thermostatic Vacuum Switch.
I could go on, but realize that if you do plug the nipple you will disable the TBV, which may not be such a bad thing.
But the real reason I responded was to ask what is the nylon tube attached to the rear carb doing ?
Is it going to the EGR valve ?
Gerry M

Gerry M

Yes the tube attached to the rear carb (top centre port) is connected to the EGR. The tube attached to the rear carb (top front port) is connected to a fitting on the upper rad hose (Thermostatic Vacuum Switch?). The vacuum retard line is unconnected & unplugged. The upper and lower ports on the front carb have nothing connected (lower port has unplugged rubber elbow). What should be connected to what and what should be plugged? Thanks.

Vacuum Lines.jpg


Country flag
I could type out the whole thing but like they say "a picture is worth a thousand words", so if you want to see the whole plumbing arrangement for your 74, here's links for catalog pages with illustrations:
Take note of BA74 on the page below:
When I had a 74, I eliminated a lot of that stuff, by trial and error.
If you decide to do the same, take one step at a time and anything that sucks air when the engine is running must be capped or plugged.
However, on your carbs there are nipples that should not be capped or plugged
The nipples that suck air from the valve cover and the nipples that point toward the cockpit..
Both of those are rather large in diameter in comparison to the others.
The others, the small ones, are fair game for disabling.
Gerry M

Gerry M

Thanks poolboy. Picture 54.php shows it all. I'm missing a fair bit on my car so I think I will take the "...anything that sucks air when engine is running must be capped/plugged ..." option for now.
I see part BA74. My EGR is connected only to the top (centre) of the rear carb. Do I need to add a connection to the lower rear carb (BA74?) to have the EGR operating properly?
I also see now that I don't have any fuel traps. What are your thoughts/experience on that?


Country flag
You really want to know what I think about the EGR.
Removing it entirely It was one of the first thing I did to 'clean up' the appearance of my 74.
Your return pipe might be so clogged it's not really performing as designed anyway.
I tell you what, stick one of your fingers inside a tailpipe and rub it around the inside of the pipe, then look at your finger.
That's the kind of stuff the EGR is returning to your combustion chambers along with exhaust "gas".
If you do remove it, plug the hole in the intake manifold with a 1/2" NPT thread plug from the plumping supply department
The hole on the cylinder head is a little harder to find..you'll need a bolt with threads about 3/4" long and 3/4-16 pitch.
You can live without any fuel traps, especially so if you have capped the nipples sucking on them.

Here's something else you might want to try..
Disable the Anti Run-on Valve (ARV) and remove the associated plumbing.
BUT start like this:
You'll have a 'banjo fitting' like the one in the middle of this picture.

Remove the hose attached to the smaller nipple and put a good tight fitting cap on just the nipple.
Drive around for a few days and if you do not experience "run-on" or dieseling when you shut down, you can continue on with the clean up.
Remove the hose that was connected to the banjo fitting and the ARV situated under the Carbon Canister (CC).
Remove the U-shaped hose connecting the ARV to the CC.
As far as the hose from the CC to the ARV nipples on the carbs, it's up to you if you want to completely remove all the hoses, or replace the hoses with redirected hoses or leave them as is. The one thing you do not want to do is cap those nipples.
Here is the nipple(s) I'm talking about.
I colored it red for the picture:

There's more you can eliminate, but for now that's enough typing for me.
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