Tell me about......... SU Carbs

You would need to take it to a half decent rolling road to have them set up properly relly.

The one advantage I love about SU's is how damn simple they are to rebuild, compare to a weber.

SU carbs are nice and simple but I've never had any experience of needing to get the car they're fitted to through an emissions test. However it'd be simple to run them lean for the test

H2's were the first 1 1/4" carbs and it's very unlikely you'll come across any. You're most likely to find HS2's which were the common fitment to all the twin carb minis, midgets, 1300 Spitfires etc though the sixties and they are an improvement over the early type but I can't remember why just at the moment. HIF's were not made smaller than 1 1/2.

You should buy a pair that have come off the same car so they will have worn in the same way and be fitted with the same jets, springs, needles etc and you at least have a common starting point. The important thing to look for is sideways play in the throttle spindle as it runs directly in the carb body - can be fixed by drilling out and bushing.

A pair should also include the necessary linkages between the two of them that sinngles obviouisly won't. It should be simple task of making different length rods to alter the distance between the carbs as the levers etc usually clamp on.

Balancing a pair of carbs is a doddle with one of the simple flow meter devices you can get (eg by Gunsons) but for best performance/economy you'd really need some rolling road time to sort needles out for such an odd application.

Hope some of that helps

i have a good set of hs4s and hs6s if interested, one pair off a 1850 dolly and one pair off a sprint
pm for details mate

You could use some Hitachi built SU's to keep it in the Nissan family. I think the smallest are 38mm as used on SSS models here. I have some for a Datsun A series (1171cc) and I think they are still 38mm ones. They use the same mounting as original SU's but area bit better made.

Wow! some great replies there, thanks very much for the info ;D

Slater> Yep, I realise to get the absolute best out of them there is no alternative to a RR, but as these are simpler than webers and the like, I fancied having a go myself.

As far as fannymoulding goes, it may be easier than first thought- the standard micra manifold is a 1-2-4 type, so I'm hoping that the manifold can be cut at the "2 into 4" section and a couple of SU flanges tig welded on, if the spacing is within the limits of the linkage of course. Things never turn out that simple though do they!

I notice an opinion of "micra engines more efficient than equivalent BL engines" and "bigger carbs would be better suited as you'd expect the micra has a bigger flow rate." Indeed the micra has a 4 port head, and revs to 6K rpm (around peak power- only 50 BHP tho).

The reason I chose initially twin 1 1/4" was because of a quote from the book:



But then the book goes on to nearly contradict itself with another table:



After the first quote I thought definitely a pair of 1 1/4"s because the most modification this head will ever get is a home port, match port and a 421 exhaust.

But after the comments on here and that table, The 1 1/2" pair sounds like a better option, and if I do decide to go for those then I also have the choice of the later HIF6, which is the smallest version of the HIF avaliable. Of course if I ever swap the motor to a "big block" 1200cc, then the 1 1/2"ers do sound more tempting- hmm.

So what do you think folks?

Everyone> Great info folks many thanks As for the linkages cheers for the info seth- if they're adaptable then thats one less thing to worry about. I do plan to fit ram pipes or velocity stacks, but i'll cross that bridge if I ever get there! as with emissions worries hitachi ones do sound nice, keeping the J theme, but part of the reason I want SU's is because of their parts avaliability, and all the knowledge that folks already have with them. good idea though! And as for bike carbs, I do have a set of mikuni's (or are they keihins? can't remember) off a CBR 600 at home, But as more information and again parts are avaliable for the su's, i'd like to try that route really.

HIF 38's are newer than HIF6's. They are as fitted to some Metros (None MG) and should be easy to find.
More likely to find a pair of HS4's already on a manifold, complete with linkages etc which you could then modify more easily.

Something like this:
cgi.ebay.co.uk/TWIN-1-1-2-SU-CARBS-ON-DOLOMITE-SPRINT-MANIFOLD_W0QQitemZ320066538650

Not sure, but I may even have a pair of these complete with ITG filters if you want me to look in the shed. Please note, this isn't why I suggested 1.5" rather than 1.25" carbs!!!! LOL

As per the above, the linkage arms are simply clamped onto straight metal rod spindles, which can really easily be adatped for different carb spacings.

Ah but that's the reason for using hitachi carbs! They don't wear out like British SU's so you don't need parts! The only bit that ever needs replacing on them is the floats as they are brass on the older ones. In every other respect they function the same as SU's (they are basically SU's made under licence) Whatever SU's you go for you will have to modify the needles yourself I'd think to suit the Micra engine. I'd think that twin 1.5" SU's would be a bit much on a stock Micra engine.

you have pm