On Thu, 20 Nov 2003, Navarrette, Vance wrote:
> Don:
[stuff deleted]
> There are other needles available for the ZS carbs, but they are
> hard to find. I would think the later adjustable ZS carbs would at least
> partially offset the SUs tuning options, but maybe not.
It appears to be a simple task to modify certain SU needles to fit ZS
cars. This is documented in the Kastner book (and likely other places).
There are only a couple of reasons to switch to SU's. One would be that
you have a set. Another more subtle reason is that the float pivot on the
SU is more favorable under hard cornering. On the ZS carbs, hard left
turns will cause the carbs to slosh the fuel and you get a goofy mixture
(I can't recall exactly, but I think the carbs run too rich). At any rate,
you loose power. BUT this is easily remedied by modifying the nylon
thingie in the float bowl (the thing that the o-ring fails on and the
carbs leak on the header!) so that the float cannot drop all the way down.
But the SZ carb is generally a good solution and you can tune to get more
power with them via needle selection.
> One thing I have already observed that makes me think that the
> SUs are better: They do not use a rubber diaphragm in the vacuum chamber.
> They use a metal piston, so you need not worry about a puncture or that
> the diaphragm will get tired or hard, affecting your mixture curve. For
> that reason alone I am inclined to believe that they are superior.
I know squat about SU's, so you could be right.
> I understand that SU has (had?) a patent on the metal vacuum piston,
> so ZS had to go with a rubber diaphragm. Does anybody know different?
They both have a number of patents covering them, as far as I know. I
believe that Triumph sourced the ZS because they were denied supply of
SU's for some sort of business/political practice. Bottom line, Triumph
needed side-draft carbs and ZS came through.
The big thing about the SU conversion is that the carbs bolt on. You just
need to fabricate the linkage.
> Cheers,
>
> Vance
regards,
rml
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