Long hiaitus -- the car was running OK and passed 2001 smog test without incident (tweaking the mixture adjustment while it was hooked up to the exhaust tester). It is still impossible to get it to idle really smoothly. The most difficult part of the smog test was keeping idle at exactly 1000 rpm long enough to complete the test. (1000 rpm is the upper limit on allowed idle speed but anything lower gives excessive CO readings.)
Then... I went to Italy for sabbatical and put the car in mothballs. Since returning, I've been waiting for some time to get it back in running order. My suspicion is that the carburettors need some overhaul. Goodness knows what old gunk they have in them. So I ordered the carb rebuild kits from Delta Motorsports.
Also found a bunch of useful Zenith Stromberg pages on the web:
July 2003: Finally got around to removing the carburettors at the adapter plates that bolt on with funky looking spring washers to the intake manifold. This job really needs a stubby wrench... Took a bunch of photos to help remember how everything goes back together.
Observations:
The big O rings between the adapter flanges and the intake
manifold were mashed and dirty. Air leak?
Other vacuum hoses also suspect.
Disassembled 1st carb. Actually... it looks pretty clean inside! Much better than I was imagining. And the needle and jet orifice look fine to me -- no visible wear. Hmmm... back to the closet to check repair history. Aha! Previous owner had the carbs rejetted in 1997. So I think I will leave jets alone and just replace all other old gaskets, O rings, etc. The overrun valve and temperature compensator were a bit grungy so have cleaned them out. The valve looks like it had the original brittle membrane. The most complicated activity was replacing the spindle seals for the throttle plate. Getting the spindle out without marring the bushings is tricky. The old seals were hard and brittle. Putting a bit of Armorall on the new seals helps them to slip into place. Reassembling the linkage... There are too many ways that all the little pieces can go together. Good thing I took pictures earlier. Really should have taken notes too.
Still wondering whether I should have put the new jet and orifice in... Enough for this weekend. Next weekend will work on 2nd carb and try for reassembly.
August 6: Both carbs refurbished with new seals, gaskets and remounted. Cranked engine a few times with spark plugs removed to get oil flowing a bit and then installed plugs and started it. After some thick initial clouds of smoke it settled into a rough idle. The vacuum hoses are plugged but not hooked up yet. Next comes some mixture adjustment, etc. But first, it looks like I may be due for a new battery.