Robert,
It's been over two years since I worked with the ZS but here's a post I
saved from one of the other BBS's. See my comments after Bobs post:
Posted 27 June 2000 at 23:09:40 UK time
Bob Fischer, Illinois, USA
Jon,
No, unfortunately it's not normal to lose that much from the damper in
that short of time. Fortunately, the fix is relatively cheap, and easy.
You need to replace the o-ring seal and star washer in the damper. The
parts you can get from Moss, Vic Brit, and many others. The seal is an
o-ring that fits around a brass male threaded piece. The threaded part of
this piece goes into the female threads of the metering needle. This is the
same piece you turn with a hex wrench when you adjust the mixture. The star
washer holds it in place against a stop, yet allows it to rotate.
1. Remove the air piston from the carb.
2. Mark where the needle meets the bottom of the air piston with tape,
so reassembly and mixture adjustment will be easier. Loosen the set screw a
little, turn metering needle with the hex wrench, and when needle is loose
take the set screw and metering needle out. Be careful with that little tiny
spring that goes with the set screw. Don't lose it.
3. Take a 3/8" brass or aluminium rod (yes, you could use a steel rod,
but I didn't want to mention it), and push it into the hole that you just
took the needle out of. Make sure the end of whatever drift you use is
square, as you'll want even pressure in the disassembly as well as
re-assembly.
4. Spray some WD 40, or other "slippery stuff" in the other end. Now
GENTLY start tapping the soft metal rod into the piston, as you are trying
to push the brass piece and washer out of the top of the air piston.
Now, the important part: No matter how careful you were, you left
scratches and burrs inside the bore from the star washer, even with the WD
40, etc. You MUST remove these scratches and burrs, otherwise the brand new
o-ring will get sliced and nicked, and you'll soon be leaking again. This is
why so many repairs fail.
Find a drill bit that fits snugly, but smoothly into the bore. Usually
just above 3/8", like 25/64" or so. Get some valve grinding paste, and smear
it on the SHAFT end of the drill. Twist the paste covered drill shaft into
the bore, and spin the piston around, thus removing the scratches from the
walls. Don't take a huge amount of metal off of course, but the o-ring does
give you a little lee-way.
Lastly, clean everything up real good, then smear metal polish -
Mothers Aluminum Polish works good - on the drill shaft and do the same
until the bore is nice and shiny.
Clean up everything extra good. Then put oil down the bore, and
reassemble with the new brass piece, o-ring, and star washer. Be sure to tap
the outsides of the star washer home. As the o-ring goes in before the star
washer, and you've cleaned up the bore real nice, it should not leak, and
should last a pretty long time.
See? Easy!!
Hope this helps. - Bob
Regarding your problem and assuming the brass adjustment piece above the
needle is moving up instead of the needle moving down, you might try
inserting the 3/8" rod from the cap end and lightly tap the rod to see if
the needle frees itself.
Also on reassembly I used a long phillips screwdriver to seat the new star
washer as it allowed the washer to flex a little while going in. Then I used
the 3/8" rod to seat it fully.
Mike
'79B w/SU's
----- Original Message -----
From: "Robert Guinness" <rjglaw@swbell.net>
To: "MG listserv" <mgs@autox.team.net>
Sent: Monday, March 31, 2003 11:23 AM
Subject: Zenith-Stromberg stubborn needle removal
> During the rebuild of my Zenith Stromberg 175 CD-2 carb (with water
> choke) on my 77 MGB, I hit a stumbling block. I cant' get the old
> needle out of the piston. I lossened/removed the grub screw on the side
> of the piston and turned the adjustment/retainer screw with the Zenith
> carb tool, but the needle will not move. The needle housing is still
> flush with the piston so there is nothing to grab onto to pull out
> except the needle itself. I am afraid that if I pull on the needle
> itself, I will bollocks up the whole works. When I loosen the
> adjustment/reatiner screw I hear/feel it "pop" or "click" after about
> three turns counterclockwise. It feels as if the adjustment/retainer
> screw is fully disengaged from the threads of the needle housing and
> adjustment/retainer screw is setting back down on the top thread of the
> needle housing. If I turn about three turns clcsckwise, the
> adjustment/reatainer screw tightens up again. No matter what I do, the
> needle housing remains flush with the piston. I "PB Blasted" it and let
> it sit for 24 hours. No change. Any helpful hints? I should note that
> the car was sitting for about 18 years. Thanks in advance.
>
> Robert Guinness
> 77 MGB
> 75 Midget
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