carburator piston spring

[tvrla]

The one fact that helps make sense of this issue is that the main jet (and thus the needle) doesn't factor into this discussion. The main jet doesn't have all that much affect on the mixture until 1/2 throttle - so remove that from the equation since we're talking about off idle. An increased velocity (thus higher vacuum) through the carb will draw more fuel from the idle and low speed jets.

[Motu]

I have a fondness for SU carbs. They were really very good in their day.

I'm not sure I entirely agree with this but I once read that Strombergs were a cheap copy of the SU and Bings were a cheap copy of the Strombergs. That they were a copy seems likely given the common diaphragm dimensions.

I like SU's - working on a lot of BMC's in the '70's and '80's they were my carb of choice.  I was taught how to rebuild them in my apprenticeship, and moving to other workshops I found most mechanics hated them....because they didn't understand them.  I never found a Triumph Thunderbird with an SU, they were all removed....because the bike mechanics didn't understand them.  I found all sorts of parts for them, but never enough to build a complete motorcycle SU.   So I would use the SU manifold on Triumph twins and fit an HS1 from a Mini - did it to several Triumphs and my Norton 600 twin.  100mpg on my T110 powered Triton.

Apparently Triumph weren't allowed to use the SU on the Triumph 2000, so the CD Stromberg was made for that car only....but then found other uses too, like the Hillman Hunter and Avenger, Vauxhall's and stuff.  When Triumph became part of British Leyland with BMC they could finally be fitted with SU's.   Not a fan of Strombergs, but happy to have Stromberg diaphragms in my BMW.

[Barry]

I had twin Strombergs on a Hunter GT and there was so much give in the mechanism that connected the two butterflies it was a miracle if you could get them both to open at the same time.

SU's are a popular mod on old Harley Davidsons

[bruce_launceston]

I had a Datsun 1600 (P510) back in the early '80's. It was fitted with twin SU carbs, I learnt to tune them with a rubber vacuum tube stuck in my ear to listen if they were sucking evenly.
They were easy enough to work on and that was before I became the owner and many time rebuilder of a pair of bings.

[Lucky_Lou]

Apparently Triumph weren't allowed to use the SU on the Triumph 2000, so the CD Stromberg was made for that car only...

The later Triumph 2000/2500 PI was a disaster which resulted in many owners converting them back to "TC" with SU or Strombergs.
Lou

[Barry]

I remember the Triumph 2500 PI having a very bad press. They could be picked up very cheaply because of that. Most early fuel injection systems were viewed with suspicion.  One exception was the Bosch K mechanical system which was extremely reliable and still works well enough even today.