Henry,
I tried mailing to the address shown on your mail message, but it bounced
back twice. Sorry to clog the whole list with this.
What year is your car? I'm not sure when the ZS carburetor changes took
place, and up until I read Larry's comments, I had never heard that any of
these carbs were completely non-adjustable. However, I am familiar with the
175s on my '72 TR6, which has adjustable needles.
At the base of the piston bore, a very small star clip captures a small
brass screw with an allen head (1/8th inch?). The screw has an o-ring (I
forget if it's at the head of the screw or around the tip) which seals oil
in the dashpot. The bottom surface of this screw bears on the head of the
mixture needle.
The hole at the base of the piston sleeve into which the needle is inserted
is smaller than the mixture screw diameter--so the mixture screw cannot be
removed from the bottom of the sleeve. However, there is apparently a
chamber between the threaded portion of the piston sleeve and the needle's
hole, into which the mixture screw can be lowered; the effect of this
geometry is that the mixture screw can be turned down into this chamber
without the threads binding, and further attempts at leaning out the mixture
just twirl the mixture screw in this chamber without damaging either the
piston sleeve's or mixture screw's threads. When this happens, there is no
discernible change in the mixture screw's resistance to further adjustment;
it just stops moving the needle down.
Similarly, above the threaded portion of the piston sleeve, the mixture
screw can be loosened until its threads are clear of the piston sleeve's
threads, and yet remained captured by the star clip. And again, you can't
really feel when this happens.
Bad ASCII Art Warning: My mailer uses proportional-spaced fonts, so this is
likely to look awful on your machine. Sorry. If you can read it at all,
this figure should show a cross section of the piston bore. The mixture
screw is shown in the center of it's travel.
===== <-- Star clip
| |
| | <-- empty space to hold mixture
screw
| | in full-rich position
< < > >
< < > > <-- Threads in piston bore
< < > >
| | | |
| | | | <-- empty space to hold mixture
screw
| ---- | in full-lean position
---- ----
| |
| | <-- Needle fits here
| |
Looking down the bore of the piston sleeve with a bright light, you should
be able to see the allen-head slot of the mixture screw. You might make out
the star clip around the rim of the bore, though I find it hard to see.
With the piston out of the carb, I think you'd find it easiest to fit your
mixture-adjustment tool into the bore of the piston if you remove the
retaining sleeve first. The purpose of the retaining sleeve on the mixture
adjustment tool is to lock the piston into alignment with the carb body as
you turn the mixture screw, thereby preventing the rubber diaphragm from
being twisted and torn. However, on my tool, the allen key is slightly
warped, making it difficult to engage in the mixture screw with the
retaining sleeve in place. With the piston out of the carb, the rubber
diaphragm is out of harm's way, and you can safely set the retaining sleeve
aside.
Once the mixture adjustment tool is engaged in the mixture screw, you can
tighten or loosen the mixture screw all day long, but it will remain
captured until you remove the star clip above the mixture screw. This is
best done with a dental pick. If one is not available, you might try the
smallest crochet needles sold at K-Mart ($1.50. I bought the whole 6-tool
set for about $5, just to be sure. Then I found a dental pick...). With a
small hook, the star clip is quite easy to withdraw; without a small hook,
it's a royal bitch. Once the star clip is out of the way, remove the
mixture screw by turning it clockwise (it's reverse threaded).
All of this information is useless if Larry's right and you have a
non-adjustable carb; but maybe Larry's wrong and you've overlooked the
mixture screw at the base of the piston bore.
Best of luck, and I apologize if my writing's tedious; I'm trying to help,
but this stuff is tough to describe.
Kevin Riggs
'72 TR6
rkriggs@ingr.com
Huntsville, AL
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