SU HS6 1.75"

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Ltriumph
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SU HS6 1.75"

#1 Post by Ltriumph » Tue Apr 19, 2022 8:30 am

Hi - I have a 1978 Triumph 2000TC, have the chance to get a set of SU carburetors, stated as HS6, 1.75" off an S - would they fit the 2000TC (if so will they need the needles changed?)
Triumph TC 2000 1978
Triumph Bonneville T120 2018

johnnydog
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Re: SU HS6 1.75"

#2 Post by johnnydog » Wed Apr 20, 2022 10:32 pm

The carbs on a late 2000TC should be HS6's - the same as fitted to a 2500S, and the inlet manifold is also the same.
What carbs are fitted at present? Are they 4 stud fixing per carb on the inlet manifold - if so, they are HS6's. If they are 2 stud fixing per carb, diagonally opposed, then they are HS4's.
According to the official parts book dated March 1975, the needles are same for the 2000 and 2500, but in the official parts book dated November 1978, it states the needles are different between the two models.
I always understood that the needles in a 2000TC were BCY, and on the 2500TC and S the needles were BDB, but I don't think you will go wrong if you fit BDB needles in them.
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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 HS6 1.75"

#3 Post by Ltriumph » Thu Apr 21, 2022 10:10 pm

Thanks for your input - yes they are the 4 stud.
Triumph TC 2000 1978
Triumph Bonneville T120 2018

johnnydog
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Re: SU HS6 1.75"

#4 Post by johnnydog » Sat Apr 23, 2022 8:36 pm

You might as well then keep your current HS6 carbs.
I presume you were considering replacing them with a view to improving performance? I would be tempted to contact Chris Witor to see if he can recommend a change of needles in a late 2000 to improve things.
For example the 2500 engine with HS6 carbs had BDB needles, but in my opinion is a little flat and lethargic at higher revs i.e the mixture was a little weak, although ok at tick over. I have replaced mine with BDM needles (as fitted to a TR7) several years ago, which made a noticeable difference to the upper end performance and acceleration, without particularly compromising on fuel economy.
BFZ needles in S also give an improvement in acceleration at higher revs in my experience. Both provide a richer mixture at higher revs than the BDB needle; however the BDM is the richer of the two at higher revs.
These aren't a recommendation - just my experiences as I felt my S was a little flat in overtaking situations, or in pulling power up hills.
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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