View Full Version : ZS Automatic water Choke adjustment

04-03-2005, 12:56 AM
Hi, I have a 1978 Midget with the dreaded Cali emissions (which it must still pass). It had a problem of starting great first thing in the morning and then refusing to restart again until the next day? I guessed it was running very rich, cherry red catalytic converter. Some research indicated the auto choke is a main cause of this problem so I rebuilt the carb and choke. Made what I thought were the correct choke adjustmens, but now the car won't start at all. I think I've gone from super rich (choke stuck wide open) to no choke at all. Any suggetstions would be greatly appreciated.

Okay, continueing my own thread. I pulled the carb off "again" and I find the intake pretty much saturated with fuel. Hmmmm, me thinks it's still pretty rich. It fired up this morning but quickly idled down and cut out, couldn't get her re-fired after that. I assume it was flooded.

04-07-2005, 07:32 AM
try checking the archives. There is plenty of feedback on ZS water chokes. May want to convert to manual choke.

04-07-2005, 09:46 AM
Hi there, when you say you adjusted the choke, how did you adjust it? There is a line on the water choke housing which should line up with the line on the plastic spacer, and with the line on the carburetor body. Unless the bimetal is bent, there's really no adjustment involved other than setting the fast idle speed. Other reasons for the choke permitting things to run rich consistently are:

-stuck vacuum kick piston
-loose screws holding the choke assembly to the carburetor
-bad gasket between the choke and carb body
-leaky choke needle valve, or bad sealing gasket

If the bimetal is bent or not calibrated properly, there's a procedure in the service manual for establishing a new reference point by boiling in water and seeing if the tang on the bimetal lines up with the existing mark, and making a new one if necessary.


04-07-2005, 10:56 AM
I'm not a ZS expert by any means. I did come across a couple of very informative articles that might help you if you are looking to do a little research. Hope this helps.
I would start by looking here:
I can also email you a pdf file that talks in great detail about the metering needle. It's too big to upload and I can't remember where I found it now. I've made myself a ZS bible out of them...lol

04-08-2005, 07:44 PM
I rebuilt the choke with new metering needle gasket, new gasket between choke and carb body, and new gasket between water temp sink. I verified the bi-metallic spring was calibrated correct and coiled proper. No leaks and all checked correct. By adjustment I ment the fast idle adjust and the throttle stop. Book calls for 2.4mm between throttle levers and choke (gap A) and .9mm between the fast idle pin and the cam (inside the choke). Those 2 adjustments are much closer than the original settings but are iaw the book. If those are set how do I adj them to get leaner.

I will go and checkout the 2 links and see if I get some help there.

Can't go with manual choke, illegal in cali due to smog inspection.

04-21-2005, 01:39 AM
Checked both links, I already had one of them and the was very informative. I know more now about ZS carbs than ever, still can't get the car to restart? I went on travel for a week came home fired her straight up. She ran for 10 mins or so, then idled down and cutout. Wouldn't restart after that. Frustrating, begining to think it's not the carb. Can the ignition (points type) cause a problem like this?
In the mean time, I've gone out and bought a Mikuni carb kit from prirace it should be here in a couple of days. I'll let you all know how that goes. Hopefully, I get it past Cali emmisions, assuming I get her running. Spring is here and she needs off the jack stands and out on the STREET!!

04-21-2005, 10:15 AM
Hi again, your 1978 Midget doesn't have points, it had electronic ignition from the factory. Not the most reliable thing in the world, but if yours is still firing it's probably okay. Before you go messing with a new carburetor, you might find out why it can't run at slow idle. Is it still running rich? Is the slow idle just not high enough (should be 800 RPM) to keep it going? The ZS may not be the most high performance carburetor, but it works.

04-21-2005, 11:06 AM
No, my 78 is supposed to have electronic. A previous owner swapped it out for the 25D points ignition. Sorry, I should have clarified that. I believe it still runs rich. I also don't think it's a slow idle problem, as it runs down even if I press on the accelerator it idles down and dies.
I had the slow idle turned up to almost 2k (accidently) and it still idled off. It's a smooth decline in rpm and then just stops.

I've looked for vacuum leaks, nothing noticeable.

05-01-2005, 01:44 PM
Well, I replace the ZS with a Mikuni racing carb and put Pertronix electronic ignition module in. YEEHAWWWW!! is she fast.
BTW, as soon as I accomplished the swap I read a doc that said if vehicle dies after warm up and is difficult to restart disconnect the carbon cannister? Haven't had an opportunity to check that yet, but it is exactly what my little midge does with the ZS installed. I plan on testing the theory later, having too much fun driving right now.

05-01-2005, 09:07 PM
Where did you get the Mikuni from? I was thinking about a weber conversion for my 76 but since weber is out of business now I don't know if I want to spend that much money on it. I know that I am eventually going to put a pertronix on it so that might be a good time to upgrade the carb as well.

Matthew E. Herd
05-01-2005, 10:06 PM
Weber is out of business? I heard from a supplier that they were on strike for like 18 months, but not that they went out of business.


05-02-2005, 07:40 AM
I read somewhere that they had closed the doors sometime in 2004. Supposedly there are a few companies that have bought the designs but as far as real weber stuff. It is getting scarce.