Lotus Europa Community
Lotus Europa Forums => Garage => Topic started by: YellowS4DHC on Sunday,October 21, 2012, 08:57:20 PM
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I'm new to this forum and have a question regarding the Europa TC I recently acquired. :newhere:
My '72 TC has the Big Valve engine with a SU carb conversion (look like 1.75" throats). The conversion looks reasonably tidy, although the throttle and choke linkage was a bit cheesy and had to be reworked. It is a Federal car, and all the smog stuff appears to have been pulled.
Is this a particularly desirable conversion? I was actually hoping for the Strombergs since I've got them on my S4 Elan and have some familiarity with them. What is the collective wisdom regarding these carbs? Should I keep them or try to find something better?
thanks
Rick
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Hi Rick, and :Welcome:
I've not heard of an SU conversion although I can't see why not as in the UK they seemed to be almost equivalents, a bit like the Dellorto/Weber thing. Having run cars with both SUs & Strombergs, I have a personal preference for SU which is nothing to do with performance, just that I think they are a simpler design that works equally well. From memory the critical things were to centralise the jets properly to allow the main piston to move freely both hot & cold. Apart from that they were pretty much "set-up and forget".
Tuning-wise there are (or were) a standard range of jet sizes with many needle options, the differences in the needles being the gradients/diameters along the length to allow differing mixture strengths for any given height to suit where your cams/engine/ignition advance needed more fuel than a slower cam/etc.
There are a few good reference books out there, a quick search on Amazon will no doubt bring up a page full. The one I had listed all the dimensions of the jets & needles together with typical applications, which made it quite easy to get a start point when installing SUs on an engine that didn't previously have them.
Brian
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Welcome to the forum, Rick. The SU conversion for the Twin Cam is new to me as well, though as Brian said, it seems like a reasonable conversion. Personally I can't offer any advice as I've had little experiance with them. Good luck with you quest, and I'm sure other forum members will have some words of wisdom for you.
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There is an article submitted by John Abbott in the "Articles and Repair Modifications" section of LotusEuropa.org on this conversion.
http://www.lotuseuropa.org/images/WorkshopManual/Carb1.pdf
http://www.lotuseuropa.org/images/WorkshopManual/Carb2.pdf
http://www.lotuseuropa.org/images/WorkshopManual/Carb3.pdf
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That's a good find Joe, someone has already been down the path !
/off topic, trivia mode
what does SU stand for and how old is the design ?
now no cheating and looking on google......
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/off topic, trivia mode
what does SU stand for and how old is the design ?
now no cheating and looking on google......
Well, I know SU stands for Skinners Union. It's an old carb, but I don't know how old... I'm guessing late 30s?? I also don't know the history behind the name Skinners Union... always seemed like a funny name for a carburettor. :o
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The founder's name was Skinner - the family was in the leather business.
The basic design principle is very old - pre-WW 1 I think, but I'd have to look it up. The SU carburetter group came into the ownership of BMC and another maker (Standard-Triumph ?) didn't want to pay royalties to BMC but wanted a constant-depression carb, so got together with Zenith and came up with the Z-S.
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How on earth do guys from your side of the pond know such detail about us Brits and our quaint little motor industry ???
Never mind, it's 10/10 and gold star award to you both ! :trophy:
The company SU is very old, vintage stuff from the 1900s and it was a shoemaker/leather family that started it going. Apparently the original Skinners Union carbs used a leather diaphragm or something, hence the connection.
Roger's right on the money with the Triumph/Stromberg connection as well, they were trying to dodge the SU patents but it was the "Skinners' Union" as a company name that has stayed as one of those useless facts cluttering up my memory ever since I heard it back in the early 80s.
Brian
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Well, the truth of the matter is that I am an Ex-Pat Englishman, retired and living in Texas where I've been for most of the last 16 years.
But I did live the first 47 years of my life in England, so it's probably not too surprising if I still remember some of what I learned back then!
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Oh, and I just remembered, there's a guy on the Elan forum with SUs on his Twinc - HIF6s I think, and a couple of others as well. This is not uncharted territory!
Seehttp://www.lotuselan.net/forums/elan-plus-f13/stromberg-carbs-t26449.html (http://www.lotuselan.net/forums/elan-plus-f13/stromberg-carbs-t26449.html)