One of the great things about SUs is that they hold up well over the years. Their operation doesn't depend on a bunch of small jets, rubber diaphrams, or gaskets, so there is little that can deteriorate simply due to age. Stromburg carbs are a similar design to SUs but do depend on a flexible rubber bellow, and so are not as reliable.

General rebuild kits can be obtained, though probably not for your specific carburetor. If you know you have 1600 Roadster carbs, then you can order a kit from Napa and the like. Z SUs and 2000 Roadster SUs also have specific rebuild kits available. Depending on the maker of the rebuild kit, it might include a float bowl gasket, various spacers and washers, a fuel needle and seat assembly, and possibly needles. Most of these parts are available individually from Nissan, and similar parts should be available from a good British/foreign car parts store.

If you are unable to locate a rebuild kit or find it terribly expensive (~$25 per kit, two needed), chances are that you can still get the SUs working well without a kit. Use gasket paper to make new gaskets for the float bowls, insulator spacers, and air filters. Clean and check the operation of the fuel float and seat. Make sure the brass floats are not cracked and leaking (there should be no fuel in them!). If you have float related problems, replace them with 1600 Roadster parts. These are now a new and improved design.

Check the throttle shafts for wear, they shouldn't leak air. If they are worn, have a machine shop re-bush them. This can cost up to $100 or so, but prices do vary, and the more carburetor-friendly your machine shop is, the cheaper it may turn out. British car shops will be especially knowledgable about this. Read Z Therapy's take on rebushing SUs so you know what to ask for at your machinist.

Dissasemble, soak, and clean the carb body and slide piston. Check that the needles are not bent by holding the piston and slide chamber upside down and spinning the piston and needle, the needle shouldnt wobble. If you plan to re-use the needles I'd suggest not removing them from the pistons because they get stuck and bend when you try to pull them out. The needle and jet can wear from sliding but you can compensate for this by raising the jet adjustment as needed. New needles and jets are a definite fix but in my experience; new needles alone may fix jetting wear problems. SU needle part numbers can be found here.

When the piston slides are reassembled to the carb, you should be able to raise the piston up and release it and hear a distinct metalic clunk as the piston hits the carb body. If the slide gets hung-up, check alignment of the slide chamber on the carb body. The later flat-top SU slides are self aligning because they have little rubber points that align the slide to the carb body as it is assembled. The earlier round tops must have the slide chamber carefully positioned. Slightly loosen the 4 screws that hold the slide chamber and wiggle it untill perfect alignment is obtained (when the dropped piston makes the clunk) and then carefully tighten the screws. Bent needles will also cause the piston to bind.

The Haynes weber/stromburg/SU tech book is a good reference if you have never dissasembled a SU before. ($12 at pep-boys). Has good info for rebuilding, synching, tuning the carbs but does not list part numbers specific to the Hitachi built carbs.

• Set the wfo throttles the same. Just open them up with the actuator rod/cable and adjust the balance screw to synchronize them. This will give you about 95% accuracy in the balance unless there is a serious engine internal problem.
• Make sure the chokes are off. Push up on the jets. Lots of SU chokes stick open especially after they have been sitting around. WD40 even works to free some of them up. They seal with o-rings. Just make sure they are off before you try to adjust the jetting. They work and work well so they are worth hooking up, unlike the DCOE chokes.
• Set the idle screws the same but only after #1 is done. Some SUs have both the linkage idle adjust off the manifold and the individual carb adjust. Set the individual ones first, then use the linkage one for the final adjust [750rpm with a stock motor].
• Find the little push rods that lift the pistons and the mixture adjust screws before starting the motor. Set the mixtures at about 2 turns out for round tops, full out for square tops. After starting use the lift pins to determine both balance and mixture. Since the lifts lean out the mix, the speed should drop. An ideal mix will actually speed up a bit before dropping, and both ought to sound the same if the throttles are synchronized.

If you are very serious about returning your SUs to Better-Than-New condition, you can go to the Z Therapy web page at www.ztherapy.com. They have links to their SU Rebuilding and other SU related services and products.

The folks at Z Therapy offer various stages of remanufactured SU carburetors. You can get a rebuild kit, get your current SUs rebuilt with new shafts, or get the whole kit-and-kaboodle done, down to authentic zinc plating of parts. Yes, it does cost, but what you get back looks to be a pretty good product. They also offer a pretty good warranty as well. If you have the means, check them out.

You might want to give this web page a look and have a chat with Joe. www.joecurto.com This site was passed on to me by a reader, 510 and Jaguar owner. You can't have too many options.

Z Therapy:

So, say you have your SUs all torn apart, but you can't figure out how to put them back together. Or maybe you bought a set of SUs but didn't realize there would be some assembly required and all you have is a box of funny looking bits and pieces. Well, you're in luck. The fellows at Z Therapy have created a few pages to help you out. This link to their site gives you a parts breakdown and basically a step-by-step assembly order of the parts. This isn't an assembly guide, but it's darn close.

Moss Motors:

Moss Motors, Ltd., America's oldest and largest British sports car specialists. They obviously know a thing or two about SU carburetors. Check out this Adobe.pdf page from their MGB catalog (You'll need Adobe Acrobrat Reader for this). It shows a good-resolution, zoomable exploded view of an SU HS4 carb, with all the parts labeled for ordering. You can use this to help your assembly woes. In addition, quite a few of the British SU parts will fit Hitachi SUs, helpful if you can't find the Hitachi-SU parts. Contact Moss Motors Ltd. if you have questions about their parts.

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