SU Carbs - ever had them?

[Arnold]

Rather than hijack a different thread I'm being nice and starting a new one. "Not another one" I hear you mutter.

The SU carb is from a day when engineers had little to work with and high aspirations (think the Apollo program and its predecessors). It is engineering genius. Simple though not trivial, relatively reliable and extraordinarily effective. But it was expensive and it was made in Britain, not here, so I don't think it was ever adopted by any U.S. automaker perhaps some smaller ones, correct me if I'm wrong.

Because they were rare U.S. mechanics were lost. They required a special tool to set and balance them if there was more than one which there almost always was. I've had them on two cars:

1968 MGB-GT - I was always ambivalent about this car. It ran most of the time. But the top did not go down. It was only $600. But the real reason I bought it was wife #1 fell in love with the wooden steering wheel.

1973 or 4 (can't remember) Datsun 240Z Datsun adopted its Japanese name Nissan and my $1,500 car (bought it used in 1978 or 79) is now worth $25,000. Would it have beaten the S & P 500 over that time. I don't know for sure, but I think so. I never drove it at top speed, but I did drive it at 100 mph from the AZ, NM border to Flagstaff one early morning when I saw all the state troopers from both states having breakfast at the same diner on the border.

Probably should have kept it. Should've, could've, would've. Sigh.

Anyway, what cars with SUs have you had or driven?

 

[Capt. Geoffrey Thorpe]

My Sunbeam had twin side draft Zenith carbs...

Remember "SU" stood for "Skinners Union" after the Skinner brothers who were shoe makers - the original carburetors had leather bellows...

 

[Arnold]

My Sunbeam had twin side draft Zenith carbs...

Remember "SU" stood for "Skinners Union" after the Skinner brothers who were shoe makers - the original carburetors had leather bellows...

Sunbeam, neat cars. I was not aware of the SU history, thank you.

 

[FastEddieB]

Twin SU’s on my 1966 MG Midget.

Funny story. I knew the Midget, bought new, was going to be slow. But not THAT slow!

Turns out the linkage between the two carbs was loose, so the car was running on 2 cylinders! Tightening a screw unleashed the beast.

A young Fast Eddie - on the left - getting ready to start a road rally from Bethesda-Chevy Chase High School in Maryland.

 

[bdtaz]

Triumph TR3(been in the family for 50 years now)
1969 MGB GT
1972 MGB roadster
1975 Datsun 260Z.

If the throttle shaft bushings aren't worn, more trouble free than most American carburetors I've worked with.

Very simple, certainly simpler than a two or four barrel "American carb". No accelerator pump, power jets, vacuum secondary, etc.

Throttle plate position establishes relative vacuum, relative vacuum establishes how far the piston moves, piston position moves the tapered needle in the main jet to set the appropriate mixture for that airflow.

Oil damping of the piston slows its initial rise to provide a burst of rich mixture when the throttle plate initially moves to act like an accelerator pump.

Like most any carburated vehicle, the engine generally runs OK no matter what but varies quite a bit more due to weather, gas, phase of the moon, etc. Starting technique varies with the weather.

Only real issue I have(same with the one barrel Carter on my old Jeep) is Ethanol trashing rubber components(main jet "bushings" on the SUs, accelerator pump diaphragm every couple years on the Jeep.)

 

[Arnold]

Glad you found the problem. From Midget to LSA, for both of us some things never change.

 

[GRG55]

Almost made the mistake of buying an MGB back in the early 1970s. Almost.

Picture, circa 1977, of my modified 1972 240Z that I gymkhana raced on the weekends through engineering school. A lot of FAR suspension parts, BRE engine parts, running on the original Pirelli CN36 tire. Spent a fun time building up the car. The paint work is mine also (I think the metallic brown was a GM 'Vette color). Stock dual SUs for the street, side draft Mikuni-Solex for off the street only (could not fit an air cleaner on the rear-most intake horn because the brake master cylinder interfered on the American left hand drive models).

Alas, don't have the car any more, but still have the Uni-Syn to balance the carbs in one of my tool boxes.

 

[Arnold]

Those Pirelli tires were noisy. I didn't buy Pirelli's again until last year.

 

[Rgbeard]

I can't count how many cars I've owned with SUs.

Two MGs, and lots and lots of Jaguars.

I recently rebuilt the two on the 1967 420.

 

[champ driver]

My current MG to date.
SU carbs are simple in operation and with only a couple of moving parts, once set they stay set.
The SU-HS4's are prone to shaft wear, not the later HIF's as much.
My brother still has a manifold and triple SU carb setup from his E Type he had years ago.
Most complaints about MG's are from people that didn't know a thing about them. MG's were, and still are in-expensive cars, many were bought by college students and repaired on a students salary. So they didn't get the best of care. Add to that, the NN that rooted around in wiring and other systems without any knowledge of what they were doing.
Most electrical issues are from bad grounds and such. See how your Honda or Toyota fair when they're 50 years old.

 

[Sac Arrow]

'71 Volvo 140 wagon. It was the folk's car but I drove it a lot. Seemed to run fine. Points were more finicky than the carbs.

 

[Arrow76R]

My '60 and '66 Volvos had twin SUs. To balance them was a pain but there was afloat type test device that made it pretty easy.

 

[schmookeeg]

Hmm... had twin carbs on my 73 240Z, but I thought SUs were only on the 1970-1972 ("round top") and my 73 and up to the fuel injected 280Z (or was it the ZX?) had (Hitachi?) "flat top" carbs.

Never could get those things to balance well. Chucked them for a pair of twin-bbl webers. What was so magical about SUs?

 

[bdtaz]

The 260Z I have parked now in my garage would have had the Hitatchi carbs(which apparently were troublesome and were poor performing due to emissions)

I bought the car as a box of parts and it came with an aftermarket 4bbl manifold that I traded for an SU manifold plus carbs.

When getting parts for the carbs, found out they were actually off a Volvo and had to get different needles to get the car to pass emissions in AZ.

SUs are dirt simple and the only headaches I have had over the years were worn throttle shafts(easy to resolve) and worn mechanical linkages that meant every time they came back to idle they ended up at a slightly different spot. No problem for a daily driver but a real pain to get to pass emissions.

Didn't recognize how easy they were until I started wrestling with early 80's American 2 and 4 bbl carbs with all of the "band-aids" added for emissions.

 

[Everskyward]

I thought this thread was going to be about some kind of fad diet...

 

[Luigi]

Had a Triumph Tr 4A, used a device called a Unisyn to balance the SU carbs. Remove aircleaner place unisyn over carb intake, set little red floating indicator in tube to mid range, set other carb to pull the same. Easy.

 

[Arnold]

My current MG to date.
SU carbs are simple in operation and with only a couple of moving parts, once set they stay set.
The SU-HS4's are prone to shaft wear, not the later HIF's as much.
My brother still has a manifold and 3 SU carb setup from his E Type he had years ago.
Most complaints about MG's are from people that didn't know a thing about them. MG's were, and still are in-expensive cars, many were bought by college students and repaired on a students salary. So they didn't get the best of care. Add to that, the NN that rooted around in wiring and other systems without any knowledge of what they were doing.
Most electrical issues are from bad grounds and such. See how your Honda or Toyota fair when they're 50 years old.

View attachment 88227

Lovely. MG. The photo works too.

 

[Sac Arrow]

I thought this thread was going to be about some kind of fad diet...

Typically, the way SU's are mounted, they would constitute low carb.

 

[Ted]

Personally I have not, although certainly been around plenty of them - mostly Jaguars and also a 240Z, few others.

Really, probably the best performance street carb out there. Good performance all through the range and simple.

 

[Arnold]

Typically, the way SU's are mounted, they would constitute low carb.

A diet reference, thanks for the skinny.

 

[airdale]

Yup. 3-carb Austin Healy 3000. Still have my Unisyn. Had some 120 series Volvos that had SUs too.

 

[Sac Arrow]

A diet reference, thanks for the skinny.

I see what you did there.

 

[Spring Ford]

SU were used on many British cars of the '60s and '70s and earlier too. Their use was ended by emission regulations that forced a move fuel injection. Pretty much every car made by the BMC Group (and successors) which encompassed many, many brands used SU. A few others too such as some Volvos. Volvo had a connection to UK manufacturing. The P1800 bodies were I believe made in Scotland for example.

Austin, Morris, Rover, Triumph, Jaguar, MG, Austin Healey, more?

I don't think any of the UK Ford, Chrysler, GM cars used them.

Later Triumph's were equipped with Stromberg which used the same principle but instead of a precisely machined piston in a bore they use a rubber diaphragm which was presumably cheaper.

The '60s devices were H2, H4, H6 which had a bore of 1 1/4, 1 1/2, and 1 3/4 inches respectively.

About 1970 they switched to HS2, 4, 6. The main difference is that instead of being held central in the jet the needle was spring loaded to bear on the jet. This apperantly resulted in better mixture control for better emissions. The jets eventually wear to a visible figure 8 shape. At least some also had a throttle return damper capsule which probably allowed a slower idle or leaner idle mixture to be reliably used by stopping the throttle from snapping fully closed all at once. I think they also had a separate idle mixture needle screw and passage instead of a big nut that moved simply the whole main (only) jet up and down.

I guess there was an H/HS8, 2 inch unit used by Jaguar.

 

[FormerHangie]

I had a 1972 240Z. It had this odd spot in the throttle pedal where it went from practically no power to rather a lot, which made it difficult to drive. I always thought that was the throttle linkage's fault. It also was extremely cold blooded and hard to start when the weather was cold.

My father bought that car for me in 1975. I had an Opel Manta, and he didn't like it very much, so he bought the Z and took the Opel and gave it to someone in his business to use. It's odd when I think back, there were a number of times he needed to make a run from St. Petersburg, where we lived, to Atlanta, and he'd take my Opel, so he couldn't have disliked It that much. The Z car was only three years old and it had a torn seat, sagging springs, and the steering rack bushings had given up and the front end shook under braking. Frankly, it was the least satisfying car I've had.

 

[asicer]

A James Bond villain was named Stromberg, one of the MacGuffins was a Solex agitator and there was a space scientist and CIA agent named Holley (different spelling). With those references, I'm a bit surprised that M's chief of staff was named Tanner instead of Skinner, Carter or Weber.

 

[mondtster]

What was so magical about SUs?

In my opinion, nothing. I suspect they have earned a reputation in the US because people view them as novel. When i got my first car that had SUs I thought they were too, because everyone made a big deal out of them. Once I started reading about them I realized they weren’t anything terribly Special or unusual.

If I had my druthers, I’d use Weber’s over SUs but there’s nothing wrong with them.

 

[GRG55]

Those Pirelli tires were noisy. I didn't buy Pirelli's again until last year.

There was nothing better that could compete with the CN36 on the course in the mid-1970s. The best ones were made in Pirelli's UK factory.

...Two MGs, and lots and lots of Jaguars...

...

Owning Jaguars would seem an appropriate introduction to keeping the temperamental ancient airplanes most of us fly in the air...

My current MG to date...See how your Honda or Toyota fair when they're 50 years old.

View attachment 88227

Very nice. BRG and tan - classic!! Looks better than showroom new. Were the wire wheels replacements for steel rims? Yours seems a bit late for the wires from the factory?

As for Japanese cars, I once heard someone describe their Mazda Miata as an MGB without the oil leak on the driveway.

I had a 1972 240Z. It had this odd spot in the throttle pedal where it went from practically no power to rather a lot, which made it difficult to drive. I always thought that was the throttle linkage's fault...

Yes, the car had a bit of a hair-trigger throttle. It would severely embarrass friends of mine who were inexperienced with it as they tried to coordinate clutch and throttle from a standing start. A smooth take-up and acceleration would come naturally with just a bit of time in the car.

...Frankly, it was the least satisfying car I've had.

Sorry to hear that.
The least satisfying car you had, the Datsun 240/260/280 Z, was the SCCA C-Class National Championship winner an unprecedented 10 consecutive years from 1970 to 1979, against marques like Porche. Bob Sharp, John Morton, Walt Mass had an unbelievable following among us Datsun petrolheads. Properly set up and maintained they were unbelievably competitive cars. Mine was very difficult to beat around the weekend cones. And it was my daily driver to get to class Monday-Friday. The driver of the Z-car that won the 1979 championship was Paul Newman. Yes, the guy mixing salad dressing in his spare time.

Mine was 10 years old and had 150,000 miles on it when some azz stole it one night.

 

[Arnold]

I see what you did there.

I thought it was important with such a weighty topic.

 

[Ted]

If I had my druthers, I’d use Weber’s over SUs but there’s nothing wrong with them.

Weber’s are definitely better racing carbs and on my list of carbs I want to own one day. But they do take more messing around with regularly and a lot of people complain about their low throttle performance. Personally I think they’re fine at that still.

 

[champ driver]

Very nice. BRG and tan - classic!! Looks better than showroom new. Were the wire wheels replacements for steel rims? Yours seems a bit late for the wires from the factory?

As for Japanese cars, I once heard someone describe their Mazda Miata as an MGB without the oil leak on the driveway.

Yeah, if you want a modern MGB with all the reliability and none of the regular maintenance more like your Honda, get a Miata.

Thank you, my MGB is an early '74, the last year of the chrome bumpers. It was semi-restored some 30 years ago and repainted this green with a new tan interior by one of the previous owners. The chrome wire wheels are not stock, they are 72 spoke and are wider than the stock painted 60 spoke wires. The 72 spoke wires are "too busy and too much bling" for some, but they came with the car and I'm not about to change them out as they haven't given me any problems.

 

[Ted]

Yeah, if you a modern MGB with all the reliability and none of the regular maintenance more like your Honda, get a Miata.

Mazda got the Miata right. One of the few Japanese cars that actually has a personality. Must be why it’s had such a long and successful run.

 

[mondtster]

Weber’s are definitely better racing carbs and on my list of carbs I want to own one day. But they do take more messing around with regularly and a lot of people complain about their low throttle performance. Personally I think they’re fine at that still.

I haven’t had any of those problems with Weber’s. Perhaps I’ve been lucky, but my guess is those who cite problems have a setup that Still needs attention.

 

[GRG55]

Mazda got the Miata right. One of the few Japanese cars that actually has a personality. Must be why it’s had such a long and successful run.

We've became adept at engineering and building cars that are "flawless". No bad habits, competent bland perfection, often aided by stability enhancing technologies, resulting in nothing particularly memorable about driving them.

Quite different from the Triumphs, MGs, Healys, Datsun Roadsters & early Zs, Alphas, Sunbeams, 'Vettes & Pony cars of 50 and 60 years ago. It was their known imperfections and quirks that gave them their personality.

@champ driver has it right. There's more memories and fun to be had wrestling the sometimes temperamental top down on the 'B' and going for a Sunday drive in the country than any number of modern performance sedans on the same route.

 

[Flyhound]

I had a 1959 Austin Healey 100/6 with SUs. I bought it after a fire had gutted most of the car. I rebuilt it and drove it for 5 years. Actually, I drove it for 2 weeks, then I worked on it for a week so the time it was actually available for driving was less than the 5 years of ownership. Back in those days (mid 1970s), in-flight music on airlines was provided by air lines piped to each seat. "Headphones" looked like a stethoscope with two tubes going to earpieces. The tubes were joined along most of their length, only spreading to allow insertion into each ear. I brought a couple sets of those "headphones" home and split the input ends from each other. I used them to tune my SU carbs. I would put one of the tube inlets by each carb with the engine running and would tune them until the air sounds from each carb matched. That provided really close tuning for the carbs.

 

[smv]

Had a '68 Midget. Would tune the carbs with a piece of tubing stuck in my ear. No need spending $$ on fancy mercury balancers.

 

[CharlieD3]

MG TF1500...
Dual SU carbs

 

[FormerHangie]

Sorry to hear that.
The least satisfying car you had, the Datsun 240/260/280 Z, was the SCCA C-Class National Championship winner an unprecedented 10 consecutive years from 1970 to 1979, against marques like Porche. Bob Sharp, John Morton, Walt Mass had an unbelievable following among us Datsun petrolheads. Properly set up and maintained they were unbelievably competitive cars. Mine was very difficult to beat around the weekend cones. And it was my daily driver to get to class Monday-Friday. The driver of the Z-car that won the 1979 championship was Paul Newman. Yes, the guy mixing salad dressing in his spare time.

Mine was 10 years old and had 150,000 miles on it when some azz stole it one night.

I'm pretty familiar with Datsun/Nissan racing history in the United States. In 1974 my father bought two Datsun 510 race cars, set up for SCCA B Sedan racing, which would now be SCCA GT3 or GT4. (not to be confused with the FIA classes with the same designation.) He raced them in the southeast starting then. My father went to Bill Scott's racing school at Summit Point, then rented one of Bill's school cars for am SCCA driver's school at VIR, where the chief instructor was Jim Fitzgerald. He and my father became friendly after that. In 1975, Dad raced in SCCA Nationals, came in second to Paul Newman at the first Road Atlanta National of that year. He went to the runoffs in his first year, but crashed in the morning warmup. The guy he bought the 510s from, Craig Ross, went on to build a 240Z for IMSA GTU racing, and I believe that their win at the Camel GT at Charlotte in 1974 was the first win for at 240Z in GTU. I got my start in 1976 going to Bill Scott's school and then an SCCA driver's school at Daytona ( on the infield course only), before going to my first Regional at Roebling Road in the one remaining 510.

We had two different 240Zs, had a Datsun 610 that my mother drove for a short period of time before handing it off to my sister, and had a 280Z that we briefly raced Showroom Stock. That was a better car than my 240Z, but it still had some shortcomings. For all these cars, they needed more brakes, especially at the front. That was common for cars in general of that era, particularly Japanese cars, but especially with Datsuns. The Z I had, had driveablity issues and durability issues that I would say put them well below average for that era, The basics were there, the driveline was solid, but the rest of the car - oy. I can't recall how many plastic choke levers I broke in less than three years I had it. The car was less than six years old when I sold it, and the interior was looking shabby, the springs were sagging starting in year three, and the steering rack bushing were shot as well, this on a car with 40,000 miles. There were five or six other repairs I had to make as well. Compared to the British sports cars it supplanted, it was quite superior, but compared to the European stuff its was not impressive.

You could convert one of these cars into a very competitive race, mostly because Nissan did racing development on them and sold the parts to anyone who wanted them at reasonable prices. Most of the things that broke on my car got removed or replaced on a racer. The L16 and L18 engines were pretty solid units and could be made to make power, especially considering they are non-crossflow. The Z engine of the time was a six cylinder version of the same design. It wasn't quite as good as a race engine as the fours since it had a very long crankshaft that didn't like very high rpms. Datsun overcame that by doing more development than anyone else, and won a lot of races.

I really liked my Opel, there are times I wish I had it back. The Z car, no, I really don't miss it.

 

[Craig]

Still have a TR-3A with the SU’s. Only thing we’ve found they don’t like in our 40+ years with that car, is sitting up and not being run. Let them sit too long and the pistons get gummy and have a propensity to stick. That little 4 banger has such a wonderful little raspy sound when everything is excercised and you stand on it.

 

[flyingbrit]

'69 MG Midget with HS2s and '63 Triumph TR4 with H6s.

I've heard the HD8 is as close to a "universal" carburetor as you can find: one of these will make almost any gasoline engine run reasonably well. The variable venturi ensures that the carb will never be too big like a conventional fixed venturi can be.

Good enough for Rolls Royce automobiles, but early Hawkers and Spitfires had problems during negative G maneuvers:

https://en.wikipedia.org/wiki/Miss_Shilling's_orifice

 

[Arnold]

Did any civilian aircraft have SU carbs?