Z-S metering needle question

[sheetsofsound]

I just acquired a 1980 convertible that sat parked in a field under a tarp for 10 years. Long story short, a couple of days spent full time working on it and she started and will run at idle. (Haven't driven it yet - no clutch master cylinder.) Carbs are synchronized.

On testing the mixture by lifting the air valve, one carb (3/4)responds as it should; the other (1/2) is so lean that lifting the air valve even a couple of millimeters causes a stall. Using the Stromberg tool, the adjustment screw is now fully clockwise.

Swapped the air valves. Now 3/4 is too lean. The needles look identical and are seated properly in the air valve, but clearly something is amiss with one of the air valve assemblies.

Question: Is this some kind of needle failure? Could it be something else with the air valve? The diaphragm is new and there are no holes I can see. The tabs are all lined up right.

I have had problems with running too rich on my other car, but too lean? Anyone else?

[Hasbeen]

Hi sheetsofsound, I'd suggest a compression test. The trouble could be carbs, but could very easily be something else.

If the rings are gummed up on one cylinder, weakening the mixture on it's carb will have greater effect.

I had one 7 which had spent only 3 years off the road, in a good dry shed. One of it's inlet valves was sticking open about 40 thou, due to a mixture of old carbon, & surface rust. This made tuning impossible, until the problem was found & corrected.

Mildred is the Zenith expert, among others, hopefully she will have a better idea of your problem.

Hasbeen

[sheetsofsound]

Hasbeen - Thanks for the suggestion. I checked the compression - all good. I also swapped the air valve with one from a junk carburetor I had in my garage which evened things out between the carbs a little. They still both run lean and they are now really hard to balance.

When I had the carbs off the car I didn't change the throttle spindle seals, so that will be tonight's job. I tried spraying WD40 to see if I could find any leaks, but none made themselves obvious. Hopefully new seals will solve this once and for all.

Postscript: The throttle spindle seals on one carb had been pressed over the spindle from the <i>outside</i>. I think whoever had done it was trying to apply the seal without taking the thing apart. I haven't the time to start her up tonight as its late and the neighbours are sleeping, so tomorrow morning I'll know if the problem is solved. It still doesn't explain why the lean condition followed the air valve from one carb to the other.