Pete O

Well I seemed to have solved the problem. What did the trick was a combination of turning the choke a little toward the "lean" direction, turning in (leaning) the idle mixture adjusting screws, and turning in the idle speed adjustment screw just a bit increasing the idle speed.

Fuel is new. The car runs beautifully when it's warmed up. I tried turning in the idle adjustment screws that I backed out in order to cure the stumble that I had at first. I turned them in 1/4 turn, and this seems to have improved the surging on a cold start a little bit, and I still don't have the stumble on take off. I think I'll try another 1/4 turn and see what impact that has.

Vacuum line is hooked up to the only vacuum port on the carb, and the advance is holding a vacuum. Accelerator pump gives a nice squirt. The only thing that I can think of that might cause surging is the power circuit in this carb. When vacuum in the throat is high, it holds a plunger open against a spring and that keeps the power jet closed giving a leaner mix. But when vacuum drops as RPMs rise, the vacuum can't overcome the spring pressure, and the plunger presses against a valve that opens the power jet, providing a richer mix. Could it be that the fast idle speed is right at the spot where the power circuit begins to kick in, and it causes an over rich mix, which causes the speed to drop which closes the power circuit, leaning the mix, causing the speed to increase, etc., etc.?

So I tried that, and it ran worse. It stalled.

So I recently rebuilt the Stromberg carb on my '51. I adjusted the choke unloader and fast idle cam , and did the preset for the idle speed and mixture adjustments per the manual . When I first installed it and started her up, it ran smoothly at the fast idle while it was cold. I let her warm up and set the idle speed and mixture per the manual. I took her for a test drive, and found that it stumbled on accelerating from a stop. I opened up the mixture adjusting needles some more, and that seemed to cure the stumble. But now when I start the engine while cold, the RPMs surge and fall, surge and fall and it does that until the choke begins to open. What could be causing this surge while cold?

I have an old Chilton's manual that goes back to 1940, and that shows the oem sparkplug for Chrysler was an Autolite A7. I imagine 1939 was similar. You can still buy these: https://donsautoparts.com/spark-plugs/catref/spark-plugs/ref/bo185/older-copper-core-spark-plug-autolite-a7

Since resistor plugs weren't developed until the '60s, a non-resistor plug would be standard for a '39. And as the last paragraph below mentions, a resistor plug delivers a lower energy spark. All the more reason not to use a resistor plug in a car that was not designed to require one.

What state do you live in that you believe that you can't take your car our for a drive? I don't care what stay at home orders the governors have put in place, this is still America and you have the right to drive your car wherever you want. When this is over, I can't wait for the lawsuits to start over how these orders have infringed on our constitutional rights.

I'm not an expert on 2 cylinder Buicks, but it looks like the new aluminum piston has a different kind of oil control ring than the original. Seems like the original set up was meant to direct oil scraped from the cylinder wall to drip onto the piston pin. Does the groove for the oil control ring have holes drilled in it to allow the oil to drain onto the pin?

I've heard that some clubs are organizing "moving" car shows, where a neighborhood is chosen, a starting place is selected, the cars show up there, nobody gets out of their cars, and then the cars just drive slowly through the neighborhood, maybe honking horns. Folks come out on their porch to watch the cars go by and wave, thankful for the diversion.

That's an unfortunate choice. What better way to pass the time than to take the old car out for a spin? It is the ultimate in social distancing. You're in your car, by yourself, with nobody anywhere near you, just out for a drive to nowhere.

Check your gas cap. The vent holes in the gas cap may be blocked.

This show has been cancelled.

I'll be there. “Social distancing” to “flatten the curve” doesn’t, in itself, reduce the overall number of people who will eventually catch the virus. All it does is drag out the number of infections over a longer time period in order not to overwhelm healthcare facilities all at once. True, by not overwhelming doctors and hospitals, lives are saved for those that require the intensive care a hospital that is not in code black can provide. And by buying some time, scientists may (I hope) come up with treatments that help and perhaps a vaccine. But there’s no guarantee that an effective vaccine will ever be developed. Eventually, even with a flat curve, ALL of us are going to be exposed to the virus at some point in the future, unless you seal yourself in your house and never interact with another person for the rest of your life. But that’s not living in my opinion. Some of us will catch it, recover and gain immunity, strengthening the herd. Some of us won’t recover. That’s Darwinism for all to see. It is a law of nature that cannot be denied despite our belief in modern medicine. I realize that this comes across as cold and heartless, and if I had friends or family who were struck by the virus, I would probably feel differently. But I think that putting aside emotions and using logic I would come to the same conclusion. At some point in the very near future, we’re going to have to decide if we want a functional society and economy, or a country populated by hermits sustained by government handouts, which by the way cannot last very long.

Check that the wire going from the power post to the points is not grounding out against the distributor body or plate. I found these cap springs on ebay. Says its for 51-55, but I bet if fits 1950 too, as the parts manual shows the same part number for 1931-1954: https://www.ebay.com/i/282585262631?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=282585262631&targetid=886140166958&device=c&mktype=pla&googleloc=1025016&poi=&campaignid=9426356127&mkgroupid=98691857674&rlsatarget=aud-762207186714:pla-886140166958&abcId=1140476&merchantid=101641758&gclid=EAIaIQobChMInNWfrvfg6AIVdOW1Ch2bcwJqEAQYASABEgItPPD_BwE