SU Carb question...

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Sal
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SU Carb question...

#1 Post by Sal » Sat Jan 02, 2021 8:05 pm

Hello there,

I’m about to buy a service kit for my SU carbs, can someone please let me know how I confirm which SU carbs I have so I purchase the correct repair kit. Is there a model code or part number somewhere on the carbs I should be looking for.

Thanks in advance

Sal

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Alec
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Re: SU Carb question...

#2 Post by Alec » Sun Jan 03, 2021 9:10 am

Hello Sal,

there would have been a small tag on the dashpots with a reference number, this tells you exactly what parts are in your carburettors. Hoever, over the years it is mor ethan likely that it will be missing.
I don't know what car you have but it's likely they will be HS4 or HS 6 carburettors (11/2" or 13/4" respectively)
Burlen Services is one of the best sites for S.U. information as they are the current manufacturer of spares.
If you tell me your car and year assuming it is standard I can tell you what carburetors you should have?

Alec
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MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration.)
Hymer 564 Motorhome.

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Re: SU Carb question...

#3 Post by johnnydog » Sun Jan 03, 2021 12:36 pm

From previous topics, it would appear that the car in question is a 1973 2.5PI , but on carbs.
It is highly likely, being a 2.5 engine that the cars you have fitted are SU HS6 carbs, rather than HS4's which were only fitted to mid range era 2000 models around late 1973 -1974.
If each carb has a four stud mounting to the inlet manifold, you have HS6 carbs; if only two studs on each carb, then they are HS4's.
Once confirmed you have HS6 carbs, then you need to establish which kind - if there is a red plastic tip about 1/2" in depth at the base of each carburettor, then you have the standard (and preferred) jets, which are adjustable externally at the base of the carburettor body, but if it has a metal base that looks like a 'top hat', then you have 'waxstat' jets, which rely on heat to control the mixture.
Waxstats carbs were introduced for emission purposes, and can be less reliable than the standard red tip variety, but can be converted to red tips easily with the correct kit. My 1976 'S' was originally on waxstat carbs, but I converted them to the red tip type years ago with the genuine SU conversion kit from Burlen Fuels.
They are also available from Chris Witor.

Here's a link showing the difference between the two on his website -

https://www.chriswitor.com/proddetail.php?prod=LZX1120

https://www.chriswitor.com/proddetail.php?prod=AUD9105

Progressing forwards a bit, if they are HS6 carbs, and you do decide to convert waxstats to red tips, you will also need this kit....

https://www.chriswitor.com/proddetail.php?prod=CW3180

My car also had poppet valves on the butterflies, which again are for emission purposes, so I did away with them, and fitted standard butterflies as I felt that the poppet valves restricted the airflow somewhat.

Chris Witor may be the best person to approach, as his knowledge of the 2000 / 2500 is second to none, and he should be able to give you the best advice relative to what you want to do with the carbs. He also can supply different needles suitable for a PI running on SU carbs for the best fuel delivery relative to a PI engine.
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1967 Mk1 2000 in Gunmetal Grey
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1976 Mk2 2500S in Carmine Red

Sal
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Re: SU Carb question...

#4 Post by Sal » Sun Jan 03, 2021 6:47 pm

So i’ve Whipped the carbs off and taken a closer look...

They are two stud with red tips so I’m guessing HS4’s, are these ok for my car as that’s all I’ve got?

Both carbs have tags on which say AUD607F & AUD607R, what does this mean?

I’m still a little unsure of what service kit I need to order or should I just phone Chris Witor with the above information?

Thanks again
Sal

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Re: SU Carb question...

#5 Post by johnnydog » Sun Jan 03, 2021 7:53 pm

Those tags indicate they are HS4s fitted to early facelift 2500 cars around 1974. The F and R only refer to front and rear carburettors.
Personally, if you plan to leave it on carbs, I would be tempted to find a set of HS6 carbs on an inlet manifold (you need the inlet manifold as they are not interchangable), as the airflow will be a lot better as the airway from the inlet manifold to the carb body on an HS6 is a lot bigger than HS4s. HS4s are 1 1/2" carburettors whereas HS6s are 1 3/4"
Seeing as you are thinking of going to the expense of overhauling your HS4's, I would be tempted to spend it on the larger HS6 carburettors instead, but I would speak to Chris Witor and get his advice before deciding which way to go.
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1967 Mk1 2000 in Gunmetal Grey
1969 Mk1 2000 in Royal Blue
1970 Mk2 2000 in Valencia Blue
1972 Mk2 2.5 PI in Triumph White
1973 Mk2 2.5 PI in Sienna Brown
1976 Mk2 2500S in Carmine Red

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Re: SU Carb question...

#6 Post by Sal » Sun Jan 03, 2021 9:39 pm

Thanks Johnnydog I’ll look into all options.

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Re: SU Carb question...

#7 Post by Mike Stevens » Mon Jan 04, 2021 11:36 am

John has given you some excellent advice but you also need to know that the ait filter arrangement is different between HS4 and HS6 setup. The HS4 has a pair of filters inside an airbox fitted to the carbs. HS6 has a longer inlet manifold so there is not room for the filter between the carbs and the RH strut panel, so there is an 'elephant's trunk' arrangement to a single (large) air filter box bolted next to the radiator.

All of this probably reads as complex, but a picture may help.
Triumph_2500S_Auto_1107_engine.gif
(Picture shamelessly copied from t'internet!)

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(1949 LandRover was blue should be light green!)

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Re: SU Carb question...

#8 Post by johnnydog » Mon Jan 04, 2021 11:51 am

Following on from the point Mike makes, the 'elephants trunk' air box on the twin HS6 carbs is getting hard to find now in good used condition, and strange as it sounds, the flexible hose connecting this to the remote air filter box on the radiator panel is an odd size (internal diameter) and can split over time, and again are not easy to source in good used condition. If you do go down the HS6 route, you may be lucky and find a complete set with the trunking, air boxes and throttle linkage still attached.
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1967 Mk1 2000 in Gunmetal Grey
1969 Mk1 2000 in Royal Blue
1970 Mk2 2000 in Valencia Blue
1972 Mk2 2.5 PI in Triumph White
1973 Mk2 2.5 PI in Sienna Brown
1976 Mk2 2500S in Carmine Red

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Re: SU Carb question...

#9 Post by Charles H » Mon Jan 04, 2021 12:40 pm

Additionally you will need the two packing pieces under the off side engine mount to give the greater clearance required for the HS6 set up!
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Re: SU Carb question...

#10 Post by johnnydog » Mon Jan 04, 2021 7:04 pm

Charles H wrote:
Mon Jan 04, 2021 12:40 pm
Additionally you will need the two packing pieces under the off side engine mount to give the greater clearance required for the HS6 set up!
I've plenty of those if required!
Register Member no. 1596

1967 Mk1 2000 in Gunmetal Grey
1969 Mk1 2000 in Royal Blue
1970 Mk2 2000 in Valencia Blue
1972 Mk2 2.5 PI in Triumph White
1973 Mk2 2.5 PI in Sienna Brown
1976 Mk2 2500S in Carmine Red

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