Don wrote:
Subject: SU vs ZS for TR250 TR6 and Kas
<Do SU's (1.75 HS6 for TR250/TR6 I guess??) have adjustable or fixed
needles/jets? It's hard to tell from my
manual.>
Don---Far as I know, the SU's have adjustable jets, similar to some of
the early ZS. The needles are fixed. (Sort of)
<On page 105 of Kas's book he talks about the ZS as if the needles are
not adjustable:
"The pre-emission ZS had a very nice fuel adjustment nut on the bottom
on the unit. Easy to use and adjust. We tried in various ways to use the
emission type carbs (no adjuster for the mixture) and were not
successful enough in our testing to fit them to the race cars." >
There were three styles of ZS fitted to the TR six. Early, with
adjustable jets (Kas' earlier preference) then the non-adjustable ones
with fixed needles and jets, and later the ones with adjustable needles,
and fixed jets. The last one came into production after Kas decided to
use SU needles, with more selections. (He later made his own, which is
for another time) By then he had adapted these needles to work in the ZS
carbs, using the method described in his new book.
<...Is there something different between the older ZS with the
adjustable jet vs the later ZS with the adjustable needle.>
There are some minor differences with some of the ports, but mostly in
the way they can be adjusted.
<On page 105 Kas describes how to modify SU needles to work in a ZS.
Sounds like an easy solution to the needle availability problem of the
ZS. Is there more to it? It would seem that a ZS with adjustable needles
and with Kas' trick of using SU needles with the ZS, it would seem to
level the playing field between the SU and ZS. Or is there more to it?>
I think the rules stated that you couldn't change carburetors, but
apparantly you could alter the stock ones. Solid needles are easier to
purchase, make, and/or re-profile than the biased style. Easy to adapt
to the air valve, using the bushing and lockscrew, which also affords
some up and down movement. Not as quickly moved as are the externally
adjustable needled B1AF's, but do-able. Duplicating a standard needle
that's had it's profile altered requires special equipment.
<Thanks,
Don Malling>
Dick Taylor
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