The bi-metal unit on the front side of the carb, (ZS 150), is simply an air path, and opens to allow additional air in when the carb body gets warm, no fuel/air mixture involved. The manual choke ZS body is slightly different than the auto choke versions body. There is a small vacuum port on the top for the auto choke. I've modified my auto choke ZS 150 to a factory manual choke, (starter box), but had to tap one of the mounting holes to install the starter box assembly, plug one of the auto choke mounting holes which went through into the bowl chamber, and plug the vacuum port with some high temp silicone. I also had to modify the linkage assembly. I bought an older ZS manual choke carb on Ebay for a few bucks, and I used the starter box, and had the parts needed to modify the throttle linkage assembly. Works GREAT! Pull the choke, and turn the key.....starts right up, and then I let off the choke a bit till she's warmed up, and it looks entirely factory stock, and good driveablity.
Don