I've been back and forth on this, so I figured i get people's opinions. Weber Vs. SU Carbs. I like the Weber for the performance, but the SU looks so much cooler. The thing is all i hear is bad things about SU. any suggestions?
SUs are awesome, I'm a believer in the constant velocity carb function. I have a single 2" HD-8 on a 108 CI turbocharged shovelhead HD that kick starts on the first kick, gets 36+ mpg on the street and runs mid 9s at 140+ on the track. The only problem with it is I have to make my own parts for it, there aren't (or weren't) many sources for tuning goodies. And the damper spring is critical - if you don't have that right, there's no way to tune the rest of it. The good news is that there are not many parts required compared to a carb like the Weber. What are you putting them on?
The biggest trouble with SUs is that there are only two jet sizes, but umpteen needle sizes and profiles. Your best bet is to spec them after a similar sized engine, considering breathing differences such as cam and headers. Or you could find some 85-year old race mechanic from England and do dozens of full throttle, high rev runs and read the plugs each time. The second problem is the throttle shaft wears out the carb body where it p***es through on each side, causing bad idle. Proper maintenance involves a drop of thick oil at that spot every few thousand miles to prevent wear, but no one ever bothered to do it, so most are totally shot by now. You can rebuild them by bushing the throttle body, and replacing worn shafts. Balancing them is not the problem it's cracked up to be, I just used a vacuum hose to listen to the flow of each one, although there's a cool tool that can do it. Stromberg made a similar carb, but not as good looking.
SU are fairly trouble free once set up fot the engine. The position of the main jet is adjustable against the taper of the needle which richens or leand the misture. You adjust it by truning the nut on the bottom of the carb. A good rough setting is to close the nut then back it out by counting 10 flats of the nut. I have a pair which have been modified running on an AH sprite I used for auto crossing. Mine are set at 13.5 flats opened. Wanting to run a bit rich rather than a lean mix and toast the valves. The trick is to match the size to the engine. like any thing else over carburation is not good for the engine.
bomb proof, simple and parts have not dried up for them...(and can be made to look older than they are)
Weber's are great carbs, but ugly(IMO) and expensive. By comparison SU's are handsome, "pedigreed" and cheap. I run triples on my daily driver and if kept dust free, oiled and occasionally balanced, they work well.
On that Mercedes 6 I would run 3 Weber DCOE side drafts and leave the guys with their "Good Looking" SU's in the dust. Far superior carb in every way!
The SU is a good carburetor, fairly inexpensive, easy to tune unless they are warped, and easy to modify except for metering needles. I do not know the current supply of off-t******lf metering needles. It used to be limited; and when we were still working on SU's, we made most of our own. The Weber is a very good carburetor, fairly expensive, extremely difficult to dial-in (unless you are independantly wealthy, or have unlimited access to a dyno and a truck load of Weber parts, or someone else has already dialed in a set on the exact same engine, and you have their calibration set). The Weber will outperform the SU if both are at their optimal tune. As far as "good looking" both are ugly compared to a set of Carter AFB's ☺☺☺ Jon.
Rivera Engneering in CA sells new SUs, with modern float bowl design, temperature compensation, sealed throttle shafts, etc. They have tuning parts. If 1-3/4 throat is big enough they are easy to work with. I personally like the looks of Webers, especially on the top of a 427 side oiler. As Carbking said, dialing them in is not for the uninitiated!
SUs are easy to work with once you get used to them. Tuning books are still out there and parts (and rebuilding services) are out there too. Google is your friend and a simple search will bring up more than enough sources and information. Here are a couple of places to start. http://www.teglerizer.com/sucarbs/ http://www.aptfast.com/ Plenty more out there if you look for it.
Been using weber's of all sorts since the 1970's - DCOE's (side drafts), IDA's, IDF's, DCNF's (Downdrafts) DGV, DGAV's (progressive Downdrafts) a**** others, and have never felt them to be hard to dial in at all. And I think they are the best looking carb ever made - very purposeful and racy looking in my opinion.
A good freind of mine had a pair of SU's on his Pinto-powered roadster and they worked great. I may be wrong (big surprise) but didn't early 240Z's have SU carbs?
Yep . . . helped a friend build a hot one back about 1970 or so (can't remember the years on those damn things!).
Actually, they were a Japanese (Mikuni?) copy of the SU. SUs are about as retro as you can get-they've looked the same for 100 years! Dead simple to work on. Do a search for Frenchtown Flyer's replica of a 30s race car that he's building. Triple SUs on a Ford 300, disguised to look like a straight 8! For a better view, look for it on fordsix.com in the "big block six" forum.
SUs are killer when you get'em right. Burlen has the parts, including needles custom tapered to your specs if you want. All three jet sizes, needles out the wazoo, all the spring rates, ad infinitum.
That's interesting since the Pinto came with a Weber design carb stock. SU's are cool and close to a century old traditional.
Hotroddon - please allow me to rephrase my comment. If one has worked with anything, including the Weber carburetor, as long as you have; one is going to have a certain comfort zone with the unit. I can certainly see how you might have very few problems with them. My comment was meant for someone who is considering using Webers (the original poster) who probably has very little experience with them. The Webers are almost infinately tunable. But that trait means that the novice (or even someone like me who has worked with almost every carburetor imaginable, but few Webers) has many ways to go wrong in selecting tuning parts. As I mentioned, if one has a known working set of calibrations, then one would have fewer issues. And I did suggest that the Weber, properly calibrated, would outperform a properly calibrated SU. Wasn't throwing rocks, just feel these are not as easy to work with as some other brands. Jon.
Jon, didn't take it that way. It has been my experience that they aren't all that hard to dial in if you take a methodical approach. They can be intimidating at first but if you get past that they are pretty easy. I can see where a person could get lost though. Naturally different people see all carbs in a different light and part of that is certainly experience. Personally, I would rather work on a Carter AFB or Edelbrock over a Holley, yet I see Edelbrocks bashed here a lot as too hard to work on. Weber's initially came easy for me and I know others that feel the same way but I have also seen some struggle. And I've owned some SU too, mostly on British stuff and they work OK but aren't overly sophisticated.
been running SUs on my scooters sence 1969,much more forgiving and easier to tune then a weber as was said riveara sells a very good carb thier KING CARB as they call it,love em instant h/p over most other carbs and u can modify them if so inclined spring very important along with oil in dampner,there r 3 main jets avail for the su with float bowl made into carb a .090.a.100 and a .115+ lots and lots of needles to play with,as for oil in the dampner remember the slower the slide comes up the slower the acceleration,i prefer just a quick spray of wd-40 on my scoots carb u get used to the clap-clap of the slide once the h/p kicks u in the ****,im putting two on a r-20 toyota motor for my track roadster,i have the address to send for a book on sus performance tuning etc just e-mail me if u want --rocket88coupe@aol.com
the ones on the early Z cars are hitachi, they bought licience to build duplicates of the originals. they are pretty easy to work on, and plenty of parts, try Z therapy for example. they also can fix the throttle shaft problem permanently. they install a patented system that puts in roller throttle shafts with bearings. they also fix the sticking choke,well mixture enrichment on an SU, problem. I know off topic but i'm putting a set on an 86 honda, No one i know has ever done this before,so everything has to be fabricated from scratch. been working on it three years. Mine are from a 72 datsun 510 sss, which was never sold here, so it's really hard to get parts. the Z ones are great carbs, but if you use a set, get the really early ones, the later ones had emissions on them which made them garbage. if you want a good tuning book,look for the book how to build and power tune SU carburators. you can find it on ebay or amazon, great book. tons of useful info in there, will tell you exactly how to set up and modify the needles for your engines.
....... unless it's worn of course, when replacing it merely brings it back to base. Actual tuning is accomplished by correct selection of the myriad available needles, a small range of springs and judicious modifications to the parts. In the HIF, the jet ends that pick up the fuel in the bowl are also available in left, center and right facing tips for tailored applications.
here's a picture,I know off topic, but these look the same as the early datsun z carbs, such as the ones on the 240z. still plumbing and cleaning up so some loose ends in here. if you run the su's get the short velocity stacks, the tall ones are pretty much for looks,or high rpm racing. the short ones will really help flow in at the edge of the carbs. I ended up making my own which are inside of the air cleaners. the air cleaners by the way started off life as airplane tail wheel hubs. this is a two litre so i can use some of the data from a lot of european two litre engines in the tuning. a lot of brittish cars used engines that size in the 70's. make sure you run a low pressure fuel regulator, and be sure to replace the fuel tubes and clamps that come out the bottom of the fuel bowls. they make modern materials that will resist the dam corn in modern gas. the old materials will disolve and dump gas all over under them. the vac***e gauges work,but are eye candy is all.
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