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TR2/3/3A Vacuum Hose Fitting Install, Any Suggestions?


Jedi Warrior
Esteemed Collective:

Has anyone installed a vacuum gauge port on their TR3A intake manifold? I've been thinking of trying my luck at tuning using a vacuum gauge, but don't have any access into the manifold. I really don't want to install a fitting on the manifold in a place (like the top) that spoils the nice looks of the manifold in my engine compartment. I'd be willing to drill and tap and install a fitting under the connector log between the carbs. I suppose I could plug the port with a pipe plug after use, so it wouldn't be so conspicuous. Any thoughts on this? Anyone use a vacuum gauge for tuning?

Thanks for any ideas. IMG_2773 (Large).jpg



Do the carbs on the TR2/3 use the same bolt pattern as say the later HS4 or HIF series carbs? If so, one possibility are the vacuum port tapped carb spacers used on BMC cars. The insulating spacer has a barbed fitting for vacuum hose connection.

See the link below for one such spacer that Mini Mania sells. I believe sources in the U.K. sell spacers for some of the other carbs. Or... you could drill your existing carb spacer and epoxy a piece of small bore copper tubing in place for a DIY version.

Vacuum fitting carb spacer at Mini Mania.


Jedi Warrior
Thanks Doug. I'll look into this. I would be OK with drilling and installing a fitting on the insulating spacer, if that's a good solution.

For those of you who are tune-up experts, would it be suitable to install a vacuum gauge on that one carb insulating spacer? Would that adequately measure vacuum on the overall intake system or would that severely bias the result to that one carburetor? Thanks for any opinions!



Jedi Warrior
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IMHO I would not bother to do this as a tuning method.
Very nice engine bay...can you post other pics of your engine bay and car.


I have vacuum gauges fitted to my daily driver and my Mini but not my Triumphs. I like having the vacuum gauge on my daily driver as it gives me an idea how to drive to get better gas mileage. I used to tune my Japanese carbureted cars with a vacuum gauge so I know vacuum tuning can be done. I never gave serious thought to tuning my British, dual carb cars with a vacuum gauge.

Our GT6 has an S2 cam in it so the vacuum readings are never what you see in the tune up guides. I probably could tune the Spitfire by vacuum since it has a transplanted single SU HS4 carb. However... again I never considered doing it with my British cars. SUs and early Strombergs with the jet that adjusts from below are not too hard to tune.

As for the location of the vacuum takeoff, yes you might get a disproportionate influence on the gauge by only having a vacuum tap on one carb. However, there is still a crossover tube in the manifold and most tuning is done at low RPM where the butterflies are almost closed so the error will be relatively small. If it really concerns you, put vacuum nipples in both carb spacers and join them with a T that goes off to the gauge.


Great Pumpkin - R.I.P
IMO a discreet plug on the top of the crossover doesn't "spoil" anything, except perhaps a point at concours. Granted, your engine compartment will be much neater than this one was, but the plug didn't look out of place to me.

Putting it underneath would show less, but be a real PITA to R&R, IMO.


Senior Member
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I have a TR-4a manifold on my TR-3a. I rigged a vacuum gauge to the PVC port. I also have vacuum ports in each of the thermal blocks between the manifold and the carbs. They all read the same. If I have a single vacuum line on the thermal block, the gauge needle jumps around more, but average is the same. To put the vacuum ports in the thermal blocks, I drilled and installed 1/8" dia brass tube. Held the tube in place with epoxy.

If you have a TR-3 manifold, I would tap into each of the thermal blocks, join them with a vacuum tee and go to a gauge.

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