GT6 GT6 Mk3 Gas & Vapor Lines

[Deleted member 8284]

I would welcome some help in making sense of the gas tank lines I have on my 1973 GT6 Mk 3. Nothing seems to match with the illustrations I see in the factory manuals I have. The vehicle is a late model (KF 21022) and I know from experience that not all the little factory installed differences on my car are documented in the normal manuals. The car has been “restored” and the previous owners were “enthusiastic” tinkerers. All in all, it is difficult to know the true story on any one part.

My focus is to make the car a reliable driver rather than be a slave to factory originality. This week’s project is gas tank lines.

Let’s start with the gas tank fuel take off. My fuel take off is from the bottom of the tank. The illustrations I have focus on fuel take off from the top though the gauge sender. I have a NOS gauge sender spare that has this set up, but the sender in the gas tank at present does not. Everything seems to work OK, but I am confused. Any guidance?

The evaporative loss system really does confuse me. I have a large canister mounted on the right rear quarter that is fed with a myriad of tubes leading to it from takeoffs on the top of the gas tank. The takeoff on the top of the gas tank nearest the filler neck leads upwards to what I think is a vapor separator tank. These seem duplicate systems. Is this correct? If I should only have the latter system, why does my gas tank have all the other takeoffs? Any thoughts?

Thanks.

Mark

 

[TR3driver]

I would welcome some help in making sense of the gas tank lines I have on my 1973 GT6 Mk 3.

PM me if you'd like a PDF file of the emissions training notes for 73. Unfortunately I don't have the accompanying film, just the notes.<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Let’s start with the gas tank fuel take off. My fuel take off is from the bottom of the tank. Everything seems to work OK, but I am confused. Any guidance?[/QUOTE]Don't worry, be happy !
My WAG would be that someone has swapped tanks at some point in the past. But as long as the end of the tube is under the fuel, it should work fine. If you need to install the sender with the pickup incorporated, cap one of them off.<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I have a large canister mounted on the right rear quarter that is fed with a myriad of tubes leading to it from takeoffs on the top of the gas tank. The takeoff on the top of the gas tank nearest the filler neck leads upwards to what I think is a vapor separator tank. These seem duplicate systems. Is this correct? If I should only have the latter system, why does my gas tank have all the other takeoffs? Any thoughts?[/QUOTE]The thing with all the tubes from the tank sounds a lot like my 71 Stag setup; which also makes me think someone has installed an early tank. But having duplicate vents and separators (the big canister is likely also a separator, at least it is on the Stag) won't hurt anything at all. Just tee them all together with the line to the canister up front, IMO.

 

[rotoflex]

I would welcome some help in making sense of the gas tank lines I have on my 1973 GT6 Mk 3. Nothing seems to match with the illustrations I see in the factory manuals I have. The vehicle is a late model (KF 21022) and I know from experience that not all the little factory installed differences on my car are documented in the normal manuals.

[..]

Let’s start with the gas tank fuel take off. My fuel take off is from the bottom of the tank. The illustrations I have focus on fuel take off from the top though the gauge sender.

I have a NOS gauge sender spare that has this set up, but the sender in the gas tank at present does not. Everything seems to work OK, but I am confused.

My GT6 Mk3 is KF11404U, & like yours, has the fuel line coming from the bottom of the tank. It has been that way since I got it in 1975 or 1976. As you say, it does not match the diagrams in the parts manuals, which seem to show the fuel line coming from the fuel gauge sender, which itself has a pickup tube & filter. The last fuel gauge sender I got (about 2 years ago) did NOT have the pickup tube, nor did the one that was in the car.

Unless something else becomes apparent, I'd check with suppliers to find out the difference & either get a sender with no pickup or just block off the fuel outlet from the one you've got. It may be that your later car had its gas tank replaced with one from an earlier car or something, which had the hole in the bottom of the tank for the fuel line, but that would be more work than an average mechanic would do (instead of just putting a plug in the hole in the bottom of the tank & using the original fuel line to the original sender, he'd have to find the correct fitting for the hole in the bottom of the tank, put it all together, etc. Like I said, mine came from the bottom of the tank & yours may have been born the same.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
The evaporative loss system really does confuse me. I have a large canister mounted on the right rear quarter that is fed with a myriad of tubes leading to it from takeoffs on the top of the gas tank. The takeoff on the top of the gas tank nearest the filler neck leads upwards to what I think is a vapor separator tank. These seem duplicate systems. Is this correct? If I should only have the latter system, why does my gas tank have all the other takeoffs? Any thoughts?
[/QUOTE]

It is so cool to have an octopus in the trunk.

I'm not clear about this 2nd tank you speak of.

The tank with all the tubes is the expansion tank. The expansion tank connects to 3 things:
1. Those little nozzles running around the edge of the gas tank
2. The charcoal canister under the hood
3. A vapor line attached to the cast chrome-plated filler neck which has the little door & keyhole for putting gas in the car

The expansion tank (part # 216821) is located inside the right rear fender.

Part #153873 is the takeoff screwed into the gas filler neck. You can probably see in the diagram which line goes from the expansion tank all the way forward to the charcoal canister under the hood. It exits the trunk through a hole in the trunk floor near the spare tire (there's a grommet in the hole to keep from damaging the plastic line).

The lines from the expansion tank to the gas tank vents are plastic, & usually just a couple of inches short of reaching the nipples to which they connect (the actual connection is made by a short piece of fuel line slid over the nipples & the end of the line to the expansion tank.

If you find you're short the line to the gas filler neck, it may be that at some point someone stripped it or broke it off while removing the filler neck to replace the short, fat gas filler hose between the filler neck & gas tank.

----

The parts manual may have a wildcard that I can't help you with. It is for a revision to the evap system at some later and strangely unspecified commission number:

I don't know if it was actually implemented, or just planned for before production ended. At any rate, you can see the changes:

1. The charcoal canister is routed to the fuel tank, not the expansion tank.

2. The charcoal canister's connection to the fuel tank is at a new vent on the tank located near the filler neck & pointed straight out. Check for its presence on your fuel tank.

2. A separator tank (part # 158511) is added (somewhere) in the line between the charcoal canister & the fuel tank.

3. It looks like the vent connector on the filler neck is not fitted, & the hole in the filler neck is blocked off with a bolt (HU0903).

4. Since the filler neck vent is no longer used, either its attachment on the fuel tank is missing, or plugged.

Edit:

Woo hoo, here's a diagram for the 1973 GT6 evap system:

It looks like the charcoal canister line does run from the canister back to the separator tank & then to the fuel tank (as in the diagram immediately above).

The arms of the octopus likely should be distributed around the fuel tank vents much as in the top diagram, excluding:
1. Octopus to charcoal canister
2. Fuel tank to fuel filler vent

 

[Deleted member 8284]

OK guys, I think you have helped me understand what I have.

Gas line/gauge sender. No problem with bottom tap, and maybe factory correct, albeit undocumented. I’ll deal with the gauge sender if (when) my existing one gives up.

Gas tank to expansion tank “octopus.” I have this configuration as rotoflex’s diagram N3 but without the line going forward to the engine bay charcoal canister. I think this is probably factory correct, albeit undocumented, as I also have….

Gas tank via separator to engine bay charcoal canister. I have this configuration as rotoflex’s diagram N4. I’m not sure I need both this and the “octopus,” but they are not incompatible.

Fuel filler overflow to expansion “octopus.” There is no line. The overflow hole at the filler is plugged.

My guess is that I have a late model car which Triumph enhanced with their full palaver of state-of-the-art emission control equipment and thinking that escaped mainstream documentation.

Unless anyone advises to the contrary, other than checking that the multitude of connections are sound so I do not risk gas leaks/fumes in the vehicle, I’m going to leave well alone.

Thanks.

Mark

 

[rotoflex]

I think that's a pretty good plan.

If you've got the components & apparent setup of the later version shown in the last 2 diagrams, I'd say assmemble it that way.

Like you, I don't see much of the point to the expansion tank & its connections to the fuel tank if the 2nd system is in place.

Transitions at the factory are strange times & produce strange results.

As long as all the lines & outlets connect someplace or are plugged so that vapor can't escape, you should be OK. Remember, non-emissions market vehicles didn't even have the evap system.

It doesn't cost any horsepower though, & there's nothing to go wrong with it, so you might as well hook it up. And the octopus in the trunk is cool. You've always got company on long trips, & peace of mind knowing that if someone gets in & tries to steal your car, the unseen octopus behind him will silently reach forward with its tentacles & strangle him to death. Agonizingly, but cleanly; no mess all over the upholstery like you get with a trunk monkey.

 

[Deleted member 8284]

Thanks all. I'll let you know if anything else crops up. Mark

 

[LarryK]

My 73 was the same, the only thing I had ever replace was the cannister. I check the lines I could see for cracks and if there was a smell of fuel and left them alone otherwise. Never wanted to fool with much as the car got up to 40mph on a long haul. Took it from St. Louis to Myrtle Beach and back on $40 fuel in the 80s. Came home and did a tune and compression test and found a split exhaust valve in #3. Still went fast and did not feel it and got good mileage. Replace the valve and went on for another 100,000 miles. Great little car, too bad Vintage Air wasn't around back then.

 

[Bugeye58]

The expansion tanks can also be converted to spiffy catch tasnks for the race car.

Jeff