Thanks for the input guys. Wasn't expecting this big a discussion. I certainly appreciate sharing the knowledge you guys have on this topic. Can anyone list for me the exact model number carbies I should be looking for so I can begin my search?

Weber DCOE 40 xxx??
Dellorto xxx??
Solex xxx??
SU xxx??

Also do all these brands of carbies fit the same manifold? Cheers.

When I get past the silly season I want to finish the custom manifold for the Single SU setup Im doing and although It wont be a full works A series I hope it goes better than a 32/36 weber setup. At least it will look better :)

fwiw in my experience with side draught carbs (which includes twin and triple SUs and webers on holdens, hemis and minis (which have a single SU by default, and cooper and cooper S models had twin SUs) is that EVERY problem people have had with them was either due to dodgy linkages (that flex and allow each carb to open different amounts, or don't allow them to return to the idle setting, one hits home, the other not quite) or carb condition itself. WIth SUs in particular, the throttle shafts are meant to wear out over time (years) so they don't chew out the carb main body (at least not much) and you can get new throttle shafts (in std, or about 5 thou oversize, so you can even ream the carb body throttle shaft holes if they eventually do wear a little). With worn throttle shafts, they leak air, and won't 'seat' the throttle plate at idle consistently, and thus you get them with a reputation for always going out of tune.

If you take the time to re-furbish them (new needle and seats as well, and new jets, heck if it is twins, I'd also make sure the springs are even, and if not replace them). You also have to do a 'drop test' where you put the 'piston' inside the bell cover thing, and push it all the way up (no spring attached) then let it go, (have a cushion underneath) - you do this to both carbs pistons/bell covers at once. They 'must' fall at the same rate as each other, and if they don't, you need to polish the 'slower' one where the piston outer rim touches (or almost touches) the inside of the bell cover things. If you don't have the spee dthe same, then one piston will rise faster than the other, and the fuel metering on throttle changes will not be consistent between both carbs as one piston will rise quicker than the other.

Once they 'match' then you can go about getting the right oil thickness to give the right accelerator pump equivalent action.

Another thing on SUs - most people think 'light' or no oil at all and the pistons rise faster and better throttle response. Not the case. As you open the throttle, airflow increases, and it lifts the piston, and the fuel will actually momentarily lean out as fuel flow takes a (very short) moment to catch up to the increased air flow. So a thicker oil will slow the piston's rise, and make the engine 'pull harder' (murdering the proper physics terminology here) on the jet, and it gives a richer mixture - the equivalent of an accelerator pump. The piston of course eventually (and it's still in a short moment) rises to the 'correct' height for a given airflow, so it doesn't pull harder on the jet, and the needle profile determines the mixture. The richness only occurs whilst the piston is rising, and that rise is being slightly slowed by the oil.

So basically you try ;thick' oil (assuming needle profile is correct) then go thinner a step at a time, until you start getting a slight flat spot when you floor the accelerator. Then go back one step (and you can mix engine oil and sewing machine oil, or use them straight, so you can make up a lot of different thicknesses to fine tune that aspect)

There are some cases where no oil at all will still produce great throttle response, but I'd suggest in those cases it is either because the carbs are on the small side for the engine, so it can pull hard and produce more than enough signal strength to get fuel flowing, or alternately, the needle profile is too rich in the lower areas, so the mixture is so far rich that the lean out that occurs as the pistons lift too quickly is not enough to be 'fully' lean and cause flat spots.

Provided you set up either of the options (grouping the SU, stromberg and other clones as one type, and the weber/dellorto carbs as the other) properly to suit the engine combo, properly re-build/replace any parts that need it, and run good sturdy linkages, you could easily run them on the street and not have to adjust them for over a year (possibly way longer).

The other related 'condition' is to always have the ignition in good shape. A weak or inconsistent spark can make it look like the carbs have 'gone off' tune

Ok here are some of the differences:

SU's work well with a moderately tuned engine and they are more tolerant then some of the higher performance carbs............CV carbs are more user friendly in that you can be pretty far off on the jetting and it will still run with out severe symptoms. In other words the car can be uber rich and due to they way CV carbs work it won't flood out if you slap the gas peddle to the floor They do use up the oil in the dash puts at a slow rate but it's a 30 second check and all of a minute to put more oil in, The big down side of SU's is flow........................2 throats vs 4.

By contrast when your running DCOE carbs you need to do more set up on the front end to get them running well, the webers may need some tuning from time to time to keep them perfect................SU's are not any better in this respect it's just you notice with Webers.

People say the same things about Flat Slide carbs that have a bog at low RPM's......it's just the way they are.......not true, sized and tuned properly they work very well at any RPM.

With all that said I do like the SU's in a motor tuned like the GX engine is..............part of it has to due with packaging for LHD cars.


Tom

This is a good topic. Can anyone tell me what the pro's and con's are if wanting to use a twin su setup on an A1200 would be, is it viable, can it be done, is it worth it? assuming the right manifold is used and the su's are correctly tuned/maintained, what else needs to be done to make it all work right?

Hahahahaha yea ,well I had to stress how good carbs are

Carbs FTMFW ! HAHA

google gave me
For the Mother F**Kin' Win

Youngin's these day have to use swear words in everything.
Whats so bad about FTW (for the win)?
haha (im sure jesse sees the irony in that...)

What on earth does FTMFW mean?

twin 40s FTMFW they are mint ,once setup there just pure awesome ,but you cant just degrease a set and bung em on

i tryed that and was pulling hairs out trying to tune them

if you start with carbs that havnt been tampered with ,have good throttle plates and shafts ,and then put kits through them and replace any adjustment screws ,like pilot screws /idle air

and a good manifold with decent linkages ,such as a bprojects kit ,awesome manifold anf the linkages are the best ive seen for a over head rail setup ,the shaft wont twist/flex like the redline ones do and the bpro kit uses the factory throttle cable which is pretty cool and means if the carbs become a problem you can just chuck a stock carby back on

well worth the time though ,twin weber/dello/solexs are mint

single flows 98% of a twin :)

220hp in this case with single 50mm

http://www.race-cars.com/engsales/oth ... 75399976/1275399976ss.htm

http://datsun1200.com/modules/newbb/v ... id=375407#forumpost375407