SU Carb or Carbs
 

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

Re: SU Carb or Carbs
 

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

Re: SU Carb or Carbs
 

Re: SU Carb or Carbs
 

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

Re: SU Carb or Carbs
 

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.

Re: SU Carb or Carbs
 

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

Re: SU Carb or Carbs
 

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.

Re: SU Carb or Carbs
 

I think I have a complete dual SU carbs/intake/exhaust set-up in my collection (...that I might also consider selling :D ) 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.

Re: SU Carb or Carbs
 

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

Re: SU Carb or Carbs
 

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.

Re: SU Carb or Carbs
 

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.

Re: SU Carb or Carbs
 

Re: SU Carb or Carbs
 

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,

Re: SU Carb or Carbs
 

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

Re: SU Carb or Carbs
 

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

Re: SU Carb or Carbs
 

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

Re: SU Carb or Carbs
 

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.

Re: SU Carb or Carbs
 

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

Re: SU Carb or Carbs
 

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

Re: SU Carb or Carbs
 

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

Re: SU Carb or Carbs
 

Bettlesr, could you or anyone else explain to me what a Claas block is? I know of B's, Diamonds, Gaz, and the German G28T.....

Re: SU Carb or Carbs
 

ctlikon0712:
I have no idea what a claas block is. Try asking winsum, he is the one who mentioned it.

Re: SU Carb or Carbs
 

Skinners Union? Anyway, the SU is a sliding venturi carb and is generally an efficient carb. Problems usually are worn out throttle shaft bushings, which will not allow you to adjust them properly. I'd use a machine shop on the throttle shaft bushing replacements for a rebuild, however the rest is very straight forward. All types of needles and seats available. Using a Unisyn to help balance them. A couple of
1 1/2 inch or larger should be great on that motor.

Re: SU Carb or Carbs
 

Your right, sorry, no coffee at that time! lol Wensum?......

Re: SU Carb or Carbs
 

Robert
There is a link to my header story above, I have been running my SUs which are 1 1/2 for only a week or so, still fiddling with them, they seem to work well, you need to keep the monifold short so they clear the hood. Gravity seems to be enough to feed them as well, I bought an electric pump but have not fitted it. As I assume your are left hand drive you can adapt the stock linkage, I had to swap the carbs as the bowl clashed with the steering down tube.
Regards
Brendan

Re: SU Carb or Carbs
 

Brendan,
BEAUTIFUL JOB! They look so perfect & at "home" there. Will you have room for the flat round paper element air filters?
I love to observe the fuel spray pattern at a steady 2500 or so RPM. You would expect to see a cone shaped flow from the needle & jet, instead, you see a fine flow across the entire raised bridge, almost as if the bridge had a razor thin slot across it. Amazing carbs & SO simple. They work on the CVVV principle. (Constant velocity, variable volume.) Bill W.

Re: SU Carb or Carbs
 

Thanks Bill
I think they look good too, Air cleaners may be a problem as the front carb gets closer to the hood. I started making some bug screens last night. I like the look of ram tubes also, air cleaners will hide some of the carb, not sure what I will do. I have found some narrow air cleaners on ebay UK
http://www.ebay.com.au/itm/150628293...84.m1423.l2649

Brendan

Re: SU Carb or Carbs
 

Brendan,
There's a lot of different configurations of the round filters, I'm sure you will find ones that will fit. Are those carbs the same bore as the early Jag XKE? The 3.8 L was 231 cubic inch with 3 carbs, so I think 2 would suffice on a Model A's 200 + cubic inch.
I hope NO one considers using some of the earlier, smaller S.U.'s as the old types with the cork jet seals & the rinky-dink choke contraptions are a pain in the butt to keep set up & synchronized & the inline throttle shaft, with it's "waffle" spring connectors are a pain. You've used the best design of the S.U.'s. Bill W.

Re: SU Carb or Carbs
 

Bill
I have 1" 1/2" carbs, I thought they might be undersized , Monkeybiker worked out the cfm and it looks OK see below.


"I run a single 1-1/4" SU downdraft on a B banger. 110CFM. Ported, shaped valves and seats, good cam, Thomas head. I've run a 94 and although it was better at the top end it was far too rich at the bottom end. I will play with carbs again but we've just rolled down to Le Mans and back running the little SU just fine. I've a pair of the downdraft 1-1/4" I want to try and also a single 1-3/4".

Let's say 200ci x max 3000revs/3456 x 0.7 volumetric efficiency - which would be pretty good for a flathead banger. I make that around 121.5 CFM. Higher revving - say 4000 and efficiency at 0.75? Maybe 173 CFM.

A single 1-1/2" SU flows around 133CFM and a 94 is around 150CFM.You're two 1-1/2" will be plenty"


Regards
Brendan

Re: SU Carb or Carbs
 

As far as I know, a Class motor is an improved Model A motor used in combine harvestors with shell bearings, oil pressure system and alloy sump.
I believe these were still being used or made after WWll and are considered highly desirable here and sell for quite big money

Re: SU Carb or Carbs
 

The G28 was fitted into Claas combine harvesters (and presumably other agricultural machinery?) and so is sometimes referred to as a Claas engine. Same thing.