Ordered the special Zenith Stromberg Needle Adjustment tool from Delta Motorsports (gee, there's a handy tool I'm going to get a lot of use out of...) and took it in the next Saturday. After reading various email tips I was tempted to try the ethanol-in-the-gas trick, but figured that California formulated gas is so clean that anything I did might make things worse.
At the shop, they hooked me up and I raised the idle speed to just under 1000 rpm (legal range is 975 +/- 25 rpm). This immediately improved emissions to the point where the car almost passed. In fact, if I could have kept the car idling at exactly 1000 rpm, it might have worked, but the idle tended to drift slowly up and down, giving a bit to much CO when it drifted downward and going over the 1000rpm limit when it drifted upward.
I removed the plungers from the carbs and gently tweaked the needles about 1/8 turn anticlockwise (leaner). This was harder than it sounds. First, the magic Zenith adjustment tool is nothing more than a long Allen wrench in a machined steel sleeve with a little roll pin protruding from the bottom to catch onto a notch inside the carburetor. The pin and notch are to prevent you from tearing the rubber diaphram while adjusting the needle. But you can't see if you've engaged the Allen wrench and the roll pin because they're at the bottom of an oil-filled hole. So you go by feel and hope you don't do any damage. Second, the engine idles badly while the adjustment tool is in place, which sends the emissions readings temporarily way up. Also, the needle is in a rubber seat and has a spongy feel with considerable spring-back. In the end, I can only hope that both carburetors were adjusted the same. Of course, making the carbs leaner also reduces the idle speed a bit. But after resetting the idle, the emissions fell within the acceptable range. There's no way I could have done this without being hooked up to the smog tester all the while.
Emissions results before making adjustments
Values of actual/(allowable) emissions
Number in square brackets [ ] is the "average for passing vehicles
in this category."
| Test condition | Speed (rpm) | Ignition timing | HC (ppm) | CO % |
| High speed | 2570 | 92 / (400) [123] | 3.15 / (4.00) [1.40] | |
| Idle | 971 | 0 TDC | 317 / (550) [147] | 6.85 / (5.00) [1.80] |
Emissions after making adjustments
Values of actual/(allowable) emissions after adjusting carbs and idle
speed.
| Test condition | Speed (rpm) | Ignition timing | HC (ppm) | CO % |
| High speed | 2440 | 51 / (400) clean! | 1.18 / (4.00) | |
| Idle | 1001 | 0 TDC | 241 / (550) | 4.02 / (5.00) |