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Triumph TR6 - SU Carb emission questions

It's becoming clearer to me now-these cars are like a jig saw puzzle that prior owners have tried to add pieces to.

Anyway, I noticed a little hose running from the rear carb to nowhere. It was kind of pushed down into the engine compartment so I hadn't noticed it. Out came the soon to be trusty Bentley Manual-two drinks and an hour or so later, I figured out that it doesn't look like the pictures. I think, actually am fairly sure, that I have SU carbs installed instead of the original Strombergs. On page 224 of the manual, it shoes the hookup of the carbs to the to various places. Mine ain't like that. Page 162 shows the Emission control, and I am sort of like that; the car is a 1971 and it has the two pipe cannister which comes out and has a filter inside it.

There is a hose from the back carb to nowhere, that I think must be intended to go to the cannister. The other hose or pipe is on the cannister and I think goes back to the fuel tank. On page 224, it shoes ession hoses going from both carbs, teeing off into the rocker cover, and going back to the cannister. I have a hose/pipe connecting the two carbs and then just one hose from the front carb that I think is supposed to go to the cannister. If so, this probably explains some of the fumes I have been complaining about.

Where can I find out about the SU carbs? Is there a place to get a new filter for the 1971 emission control cannister (Moss and British Victoria don't show it as being available) or should I spend $89 bucks on a new 3 hose cannister and close one outlet off?


Stromberg vs. SU, how to tell them apart, a quick primer:

The carb dashpot on the Strombergs is short and squatty with a protrusion running along the raised area in the middle part of the body where the damper screws in. The float bowl is held to the bottom of the carb body with six screws, there are elongated oval temperature compensators canted at an angle along the side of the carb body on the forward facing side of the bodies. The choke cables act upon a lever that is part of the cold start valve on each carb, this valeve is on the rear facing side of the carb body.

The carb dashpots on the SU carbs are taller and smooth. If you have SU carbs fitted, they would most likely be HS6 (6 indicates a 1 3/4" carb, an HS4 would be 1 1/2") units. The HS6 carbs have separate float bowls mounted off to the outboard side of each carb body. Running from the bottom of each float bowl will be the flex jet. It will look like a tube running over to a right angle piece that goes up into the bottom of the main carb body. The choke on a HS6 operates by being connected through linkage to the flex jet and actually lowers the jet to enrichen the mixture.

Two other, but not likely SU carbs you might have would be the H6 and the HIF6/HIF44. The H6 was an earlier carb and was used on the TR3, early TR4, a host of BMC cars, etc. Here the float bowls are again mounted off to the side, but the fuel flow is not threw a flex jet, but through the ports in the bowl and the body to the jet. The jet has hard linkages to lower it for cold start enrichment.

The HIF series were later emission control varieties. For these, the carb body was rather squarish as the float bowl was now incorporated into the carb body (HIF, Horizontal Integral Float). The float bowl cover is fairly flat, unlike the well of the Stromber, and is held on with four screws at the corners of the bowl cover. Even though you cant see it from the outside like on the H and HS series, the jet is physically lowered to enrichen the mixture. The HIF44 was metric version of the HIF6. This is probably the least likely of the bunch for you to have. Not that many cars for the US market were fitted with the HIF6 carbs. Even though the HIF series was geared toward emission controlled cars, that series has a lot of performance potentia and I personally find them a bit less "fiddly" than the H, HD and HS series. The first thing to do with those carbs is to remove the poppet valve butterfly and replace with either a non poppet valve one or cut the poppet valve out, weld to fill the hole and blend the weld smooth. Of course that is true on any of the later HS series with poppet valve butterflies too.

So there you have it, unless someone fitted it with some of the Japanese clones like those on the 240Z or the Weber dual DGV conversion, you should now be able to go determine what you have on the car.

The cannister is actually filled with activated carbon. One of the tricks I read about here was to recharge the cannister with aquarium-style activated carbon for just a few bucks. Take a good look - the cannister unscrews close to the bottom, I believe.

'73 TR6
has a garlic jar instead of a cannister
Brent B

I don't even have a garlic jar. sigh.

John and I seem to be among the few with the 'performance enhanced' carburetion setups (insert grin here) so we're going to chat this weekend and see if we can't get his car running a tad better.

I suspect that the mixtures are a tad on the rich side since he smells exhaust so badly. I've gotten my SUs to where they are running a nice light brown after a "high speed" run and shutoff for a plug reading. No exhaust smell now at all.

Did I mention I LIKE the SUs? btw, I was told by Joe (the SU expert) that my carbs would never work with my car since mine have the TR3 style (canted) float bowls.

Shhhhh, don't say that too loud, the carbs might hear you. They just don't KNOW they're not supposed to work.

Jim Deatsch

Thanks, all. Jim, I'll email you from home after I see what you have to say and probably call you. It is nice for stupid people like me to be able to get help.

By the way, could someone with a 1970 or 71 look at the cannister and tell me how the hookups look. I think, and it isn't like the pictures because of my SUs, that the "vapor pipe" is the one that runs back to the gas tank. Although it is not clear, it looks to me like the mystery hose from the rear of the rear carb ought to be connected to the other outlet on my two outlet cannister. If this is way wrong, someone stop me or I'm going to try it. The problem may be that the original hose for the webers fit over the cannister outlet perfectly, but the "mystery" hose from the SUs is too small and I will have to make an adapter.

"original hose for the WEBERS?"



Now I'm REALLY lost. I wasn't aware (after my HOURS of research, honest, that we ever had Webers).

I thought they were ALWAYS ZSs but then I'm no expert as we've all learned in the last month.

Jim Deatsch

Save yourself a lot of time because there is help out there. The saying "a picture is worth a thousand words" is true here. Go to
and on right top of page is catalogue request form. Get the 2 catalogues (Volumn 1 and 2)and you will not be sorry.

Also you might have seen in past threads that a lot of use refer to these catalogues when asking questions. eg. PLATE BF shows 70/71 Emissions breathing details. BF(#)1 is the carbon canister itself. When you get the books you will see what I mean.
PLATE BL5 is the little hose you are talking about and connects to the back carb (ZS carbs) and connects to the distributor vacuum retard. ( so stop not do that:)
The carbon canistor is no longer available and is worth its weight in gold.
John, do you have webers or SU carbs?
Rick C
Rick Crawford

My '71 (#20620 built in December '70 with 94,000) appears original and complete, has the canister, etc. The very small hose from the bottom of the rear carb 'wants to be' connected to the distributor vacuum retard. There is no distributor vacumum advance hardware found in later (& earlier?) models.

Even with the excellent TRF books, I think Triumph was having a lot of fun at this time playing with ignition/vacuum/emissions. Ours is almost too simple!

I said 'wants to be' because the small hose was hanging loose at the carb end (ZS's) when I bought the car in April. It ran worse connected! I plugged the ends and attached it for now because it has been Summer and as long as it runs good I'm not doing anything until I have the time to sytematically go through the ignition and carbs.

EC Smith

Oops, dyslexia! My '71 is CC60260LO. - Charlie
EC Smith

Whoops, sorry. They were never Webers. They were Stroms, or at least that is what stock was. I made a mistake, probably because I had looked at a bunch of stuff in the Moss catalog and on line. The current carbs are SU's, because they say so on the outboard float bowls.

I have the Roadster Factory catalogs downloaded, but they are not the same, apparently, as they don't show this detail The Moss catalog does show the original 1971 setup with the stock carbs. I also have the Bentley manual, which is the same as the Moss picture. Moss shows a hose from each carb, with a tee fitting which goes into the breather assempbly and another tee fitting which branches off to the cannister.

On the emission control page, Moss shows for the 1970-71 TR6 a vacuum retard connector and pipe. Obviously, that is for the stock carbs also. What does the vacuum retard do in connection with the rear carb and how come the other pictures for other years show an advance as well as a retard? Now I'm confused again.

I think I read someone's post somewhere that the vacuum retard is actually intended to retard the ignition at tickover (idle) and have no effect at higher RPM's. That does not seem to fit with my experience with it.

I have the printed catalogs and haven't looked at what TRF provides for download. I know that the information from different sources (Moss & VB) does not match. (At first I thought I had some other variation or PO invention, but now believe that my '71 has an original setup.)

I just popped the bonnet to look. A large bore (half-inch?) hose runs from the top left (inboard) side of the rear carb (at a 45 degree angle) to a T-fitting. At the T, one hose leads to the crankcase vent (valve cover) and another hose goes to a second 'T'. From there, a hose connects to a port on the front ZS carb (like the rear) and the hose to the top of the charcoal canister.

The only other fitting on the canister runs all the way back (and around the interior of the boot to the fuel/vapor reservoir in the right rear (originally riveted into the wing.) The fuel/vapor reservoir is then connected to an 'X' fitting that vents the fuel tank from two points and the filler neck.

The canister has two protrusions on the bottom that look like they should connect with something. Based on my examination and research, they are sealed from the factory and may be 'punched out' for some other applications.

What is the original complaint? Gas Fumes? Just after bringing home my new toy I replaced all the vacuum lines (all were loose and hard with age), rubber parts of the fuel lines and tightened every fuel fitting. That got rid of my fumes.

I hope this helps, but my philosophy is "If it runs well, drive it!"

Have fun,

EC Smith

I think I deleted my first attempt!
EC, what you describe sounds like the original carbs as shown in the Bentley manual.

What I have, with the SUs, is a hose connected the two carbs from about 10:00 on the rear carb to about 2:00 on the front one, looking down from above. Under this hose, on the rear carb, is a hose which connects, for now, to the distributor. (This was my mystery hose).

Then, there is what I think is the fuel line going into the front fuel float, with a line from that float to the rear one. That's it for the carb plumbing!

What you describe is exactly what I have and is correct for 1971....Plate BF. You are absolutely correct...I think Coventry was going buy the situation..."well what do we have in stock this week to put in as emission control stuff".
Interesting the "X" pipe (I have this also)was only used for a very short run on the production line. I have yet to see in print this set up ( with the X pipe). My retard hose is plugged also but still there for originality. (This set up of the hose(s) is also correct in TRF Plate BL for early and later '71s).

JohnB, I do not know what the download version looks like but the hard copy is correct. Plate BF is exactly what Charlie described and is exactly what I have. An important point is that in order for this system to work properly, you must have all the RESTRICTORs in place.
JohnB, unfortunately (some would disagree with me) you are not original so I do not think any book or picture will help you. There are others on this BBS that have changed to SUs and hopefully they will step in and tell you there set up. What you say about the fuel line sounds correct. The other piping is for emissions and should eventually connect to the carbon canister. You mystery hose is as what has been said above...but that is for ZS carbs not SUs. I am not familiar with SUs so do not know if what you have done is valid or not...HELLO SU owners.....Jim????
Good luck and for sure you will get her running good.
Rick C
Rick Crawford

This thread was discussed between 05/09/2003 and 06/09/2003

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