SU Carb or Carbs

[Robert]

Does anyone have experience running SU's on a Model A? If so, which type is compatable/modifications? Does anyone have any manifold fabrication suggestions? I'm looking to run either one or two carbs on my Model A based speedster. The only major mod to the engine is a Snyder's high compression head. Besides Model A's, I am 'cursed' with a long time interest in English cars so SU carbs are not strange to me. Any help is greatly appreciated. Thanks, Robert

[Kurt in NJ]

Probably the most reasonable ones to find are midget/sprite, and mgb, I have both types and have thought of the possibilitys, they have a variable venturi that adjusts mixture to airflow so too large isn't as much as a problem as with normal carbs---I saw thislink that lists some of them, the earlier ones used in the 50s and the first year or 2 in the 60s have cork seals to prevent leaks---probably not good choices, the ones used in AH3000 are larger (4bolt) and have a rubber that probably won't like modern gas for long and are more rare and $$ ---you would want to follow the mg manifold with a balance tube between them, the mg maniflod doesn't fit well to the A block and ex manifold

Here is alink with an incomplete chart of mgb and midget carbs - http://www.teglerizer.com/mgstuff/SUcarbs.htm

[BILL WILLIAMSON]

As an ooold Jaguar mechanic, I would use 2 S.U.'s from a 3.8 Litre X.K.E. as they would be about right for a 200+ cubic inch Model A. They're a simpler, more refined version than some earlier versions, with a much better choke system & much easier to adjust. I would use them without an equalizer tube, as you can adjust them down to a gnat's eyebrow They're a beautiful carb & oh! so SIMPLE! Bill W.

[wensum]

I know of two speedsters here in New Zealand, one with twin SU's and the other with twin Strombergs off an earlier Holden.
The owner with the twin Strombergs claims to have tried twin SUs without success, but the owner with the twin SUs races and drive long distances with great success.
In fact both cars go very well!
I think the twin SUs are 1 3/4"
Keith

[dumb person]

Is this link any help? http://www.jalopyjournal.com/forum/s...d.php?t=720811
The thread starts off as exhaust but quickly turns to the carb' in question. Personally i would use only one but i am weird.

[Terry, NJ]

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I had SUs on my TR3, Spitfire, and my Jag. Worst carb of them all! I hated them! Hard to adjust! Hard to synchronize, easy to go out of adjustment and I never liked putting oil in them every 30 days. Get an American made 2 barrel, Stromberg, Carter, or even a Rochester and save yourself a lot of grief.
Terry

[2manycars]

Like a lot of model A stories, the SU carb is a great carb when not all worn out and needing rebuilding. I have a large single SU on my supercharged MGB, and have driven it many thousand miles in the past 3 years without touching it at all. It is one of the best carbs ever designed.

[BRENT in 10-uh-C]

I think I have a complete dual SU carbs/intake/exhaust set-up in my collection (...that I might also consider selling ) that came off of a Model-B racer . Either way, I can probably post some pix of it if you are interested in just seeing what it is.

[MARVIN, CT]

Saw a picture a while back of a 60hp in a boat that had four SU's on it. Would look quite fitting on my 60hp that I put in my '52 MGTD. Marvin

[Keith True]

For SU parts,repair and info there is a fellow in New York named Joe Curto that is very helpful.Most SU carb problems are SU owner problems.They turn out to be ignition problems,valve problems,filters,pumps,etc.They are almost a primitive carb.They really are a set it and forget it type of thing.If they are sucking the oil out of them they have internal problems,usually caused by somebody getting carried away with cleaning the piston/dashpot bores and plungers.I've had SU's that I've had to change the oil in because it was so old it turned to grease.I've really only worked on one SU problem that was an actual carb problem.The rest were other problems that were made worse by guys fiddling with the SU's.I worked on a Daimler SP 250 that the owner was sending to the shop every month to get the carbs set up.That's just not right.Turns out the dual point distributer was running on one set of points.But,if the shop monkeyed with the carbs it would sound better for a while.I can sit and think of a dozen more problems that had people tearing into their SU's when there was nothing wrong with them.They really made a slick carb for a Harley too.Then the S&S came out and everybody went to them.If I was going to use anything other than a stock Zenith,I would use an SU.

[Jim Brierley]

I've never run them but they should do well. Keep in mind that the A has big cylinders and needs a big carb to feed them. I am running 3 of the little Stromberg 81's on my speedster, and they do well both in the power and the mileage departments.

[Marco Tahtaras]

I have limited experience with SU carbs but would think the Jag carbs would be a bit much. With that said, when I was about 18 I had an XKE roadster for a short time with triple SU HD8 (2") carbs. They were a dream for setup and performance. They were simple to adjust, sync, etc., and required very little after doing so. However it certainly helped having the factory shop manual which I still own.

On a Model A engine with a mild boost in compression but otherwise stock, it won't be able to efficiently utilize much in carburetion but I like the idea of SU side draft carbs and have thought about it.

[mmindling]

Have a 71 RR Silver Shadow Coupe, which runs two SU carbs. They are great carbs - very simple and easy to adjust, very understandable. Synchronizing them is more a matter of the mechanical linkage being tight and properly adjusted, than a matter of individual carb settings. For the settings, I turn each carb adjustment to zero and then set them to the factory recommended set ups. The linkage, however, is another matter. There are a number of calibrations to pay attention to in order to be sure that the movements of the throttles are identical.

Using them on a performance Model A?? I'd recommend it, but pay attention to getting the proper intake manifold and be sure the linkages to each carb are proper. There are several publications on tuning SU's.

For now, I'm keeping the Zenith double venturi on my e28. It works fine.

Regards,

[d.j. moordigian]

Originally Posted by BILL WILLIAMSON

As an ooold Jaguar mechanic, I would use 2 S.U.'s from a 3.8 Litre X.K.E. as they would be about right for a 200+ cubic inch Model A. They're a simpler, more refined version than some earlier versions, with a much better choke system & much easier to adjust. I would use them without an equalizer tube, as you can adjust them down to a gnat's eyebrow They're a beautiful carb & oh! so SIMPLE! Bill W.

I did some without the balance tube...it didn't like it. Ran better stock.
Even tried it with a small hole...no good. I think the MGB's or Tr-4's, Su's
are a better choice. Have a set at home for my B engine someday.

I like Skinners Union carbs...As an oold Jaguar mechanic...LOL

[BILL WILLIAMSON]

Originally Posted by d.j. moordigian

I did some without the balance tube...it didn't like it. Ran better stock.
Even tried it with a small hole...no good. I think the MGB's or Tr-4's, Su's
are a better choice. Have a set at home for my B engine someday.

I like Skinners Union carbs...As an oold Jaguar mechanic...LOL

Yep! designed by a plumber in Jolly Old-------Bill W. (An even ooooooolder Jag fixer!)

[wensum]

Attached is a photo of an A with twin SU's which goes particularly well.
As you can see, it has a Riley head and the basic block is a Claas which is an improved version of the model A

[bettlesr]

I have a pair of HIF4's I am planing to put on over the winter. My son is going to weld me up a manifold and equalizer tube. I have a .100 over 7:1 engine with a touring cam. Hope they work out.

[Lawrie]

What about a carb from a Harley,they are ment to run on gravity feed, and will feed a 80 cuin eng at twice the RPM of and A,and should be OK on modern fuel
Lawrie

[Robert]

Thanks for everyone's input. By chance,I found a set of 1 1/4 SU's from an A/H Sprite that I had stashed away many years ago in my warehouse-started welding up an intake last night. I will keep the 'Model A' world posted on my progress. Cheers, Robert

[wensum]

I have a Daimler SP250 which runs on two 1 3/4" SU's, (2.5 litres) a 3 Litre Lancia Lambda on a single 1 3/4" SU and a Vauxhall 30/98 on two 1 3/4" SU's (4.25 litres)
I think the SU's you are thinking of using might prove too small?
Keith