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MG MGB Technical - Mixture to rich??

After several problems, all at the same time, and several threads (thanks to all that assisted), I am now faced with a mixture that is way to rich. I have a 76 MGB with a ZS carb with all the smog equipment removed. Currently it will start but runs very slowley with no power and very rough. If I lift the air piston it will gain RPM's and smooth out slightly, but gives off a large amount of smoke (grey and light black). Here is what I know: the fuel pump is good (3lbs psi), I am getting a good spark to all plugs and the elect is strong and the vacume lines (char. canister is clear). I am planing to pull the carb next, check the floats, needle etc... any other suggestions??? Additionally, the pin below the air piston is good however the adjustment screw (access gained through the top of the piston) I think is striped and may also need replacement (I have read the how to's on that). All comments are very welcome.
Neel
N Choate

You can check the metering needle without removing
the carb. Remove the four top screws, then the
cover, spring, and air piston. You can then turn
the adjuster and see if the needle moves up and
down.

A good starting point for the needle is with
the needle shoulder flush with the bottom of the
air piston.

Ronald

Also, at the same time you can check the
diaphragm for tears -- a leaking diaphragm will
also cause very rich running.
Ronald

Neel. My experience with the Z-S is very mixed. When they run well, they are marginal. When they run poorly, they are a bear. Kind of like the old boy who kept hitting his head with a hammer. When someone asked him why he was doing so, he answered, "Because it feels so good when I stop". All of my RB cars have been converted to the Weber DGV because it is a basically good carb (but not a great one) and is acceptable to the emissions people here. My first choice would be to use twin SUs and there is a great deal of information on both the Weber and SU conversions in the archives. Time to quit hitting yourself on the head (trying to tune a 20+ year old carb) and feel how good it is when you stop. Les
Les Bengtson

Les, great comment!!! I am considering it, besides I have a big knot on my head. Thanks to all, I did check the needle and it is flush, but does not move when I turn the allen adjustment screw (great news...). The diapharm is new, replaced yesterday (praying that was the problem).
Thanks again.
N Choate

Neel. The lack of adjustment was one of the many problems I ran into in trying to set up old Z-S carbs for emissions testing. The adjusting screw is supposed to be held in place with a star washer which holds it in place and allows the needle to be moved. Most of the ones I have examined no longer worked properly and you could not adjust the needle upwards to set the idle mixture. There are rather few needles available for the Z-S, but the later cars used a leaner needle than the earlier cars. There was also a "high altitude" needle generally available. I had one installed in my 79B back in 81 when I left my car with my wife while she attended a school there. They still had dealerships back then and the dealer's shop swapped needles while we were shopping in the area. So, there is a small selection of needles available and Joe Curto probably has some in stock, as does Moss Motors. You might want to start by looking in the archives on this subject. There is information on how to remove the adjuster from the hollow tube, how to replace the rubber O ring which retains the oil in the tube and the various needles and how well they have worked for people. But, the most common solution to the problems of the old Z-S is replacement with a different carb. There is a recent thread, maybe still active, about replacing the Z-S with an HIF-6 or HIF-44 (same carb, one in fractions of inches and one in mm for the venturi size). I have little experience with the HIF series, but what experience I have has been good. I have a great deal of experience with the H and HS carbs and that experience has been uniformly excellent. Good luck with the problem. Les
Les Bengtson

In case anyone is interested, during inspection of the carb. (ZS) I found that the needle at the bottom of the air piston is good (spring and pin in tack), however the adjusting screw (the allen nut/screw inside the oil area of the piston was not working. I removed the nut (by using the method suggested in the archives, (put oil in the tube and press the retaining star washer out). I am not sure what I was suppose to find, however the allen screw was there with the o ring attached. The allen screw has fine screw threads, but that connect to nothing! Therefore, I could turn the screw all day long and it would just spin. It did not have anyway to connect to the needle to push it down or pull it up! I will be going to my best shop/parts house on Monday, but can anyone tell me how it is suppose to look? Is the screw broken or am I missing something on the needle or am I totaly lost?
Thanks
N Choate

To get the needle back onto the adjusting screw:
First reinstall the screw with a new o-ring.
Insert the needle holder as far as it will go
into the bottom of the air piston. Turn the
adjuster clockwise (looking from the top of the
piston) until the needle starts moving up.
Re-insert and tighten the grub screw with the
needle holder properly aligned.

Note that if you turn the adjusting screw
too far counterclockwise, the needle will fall
out of the adjuster and can't be raised again.
Ronald

Neel- Over the dozen or so ZS I've had the pleasure of wasting alot of time with, half were diaphram tears ( literal). Last one was in a "wrinkle" so small it was missed first looksee. Give it up and get on with a DGV Weby, orSU.
vem myers

Neel,

I don't know much about the ZS because the PO had it removed in favor of a HIF44. One of the things you mention in your first mail however makes me question if the removeal of the airpump etc. is done well. I'm currently working on this and find a lot of holes to be plugged and a lot of things to think about to have everything working properly.
If it's not done properly you can adjust your ZS untill X-mass but with no good result.
Just a suggestion.

Good luck
Carl
C. J. Gaasbeek

Neel,
I had similar problems with my '79 with the ZS carb. The problem turned out to be that the jet was worn out, so no matter what I tried or replaced, the car still ran too rich. I ordered a replacement from Moss, and after very carefully punching out the old jet and re-fitting the new one, the car starts and runs great. You might want to check it out if you are still having problems.

Mike
Mike H.

Thanks for the info. I found that the needle and adjustment screw were bad (the threads were chewed up, most likly was cross threaded and forced into position). Now I have new parts will re-install the adjustment screw, needle, etc... also will replace floats, jet etc... Then if I have problems I will be ordering a new WEBER!!!

Neel
N Choate

This thread was discussed between 31/05/2003 and 03/06/2003

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