Not sure what's happening, but I have had to rebuild the carburetor on both my Cadillac and Lincoln in the past two months due to them stalling for no apparent reason. I took both carburetors apart thinking I would find something due to the ethanol laden gasoline or some contamination but found nothing in either carburetor. However after replacing the needles and seats and accelerator pumps they both seem fine.
Jon, I have had the same problem last 2 months with my 53. starts perfectly, fast idle, etc. stalls when going 30 or 40. at random times. let it sit for 5 minutes then runs again. will check needle and seat, acc. pump also. does it with electric pump or mechanical pump. so it must be carb. or maybe a bad tank of gas. Dave
I believe there's something being done with reforming of the gas today. I still think that the gas companies have more than 10% ethanol in our gas supply they're just not telling the public. I feel like it's more than that to be honest thus causing havoc with our cars.
I even notice that I have to enrich the idle mixture screws more than normal because of how much ethanol is in our fuel especially out here in CA. Or whatever else they're putting in the fuel supply making it worse, but I've definitely noticed the reduction of performance and how often it seems like carburetors are being affected more lately from the crappy gas being used now.
Alcohol content is most likely the issue. 15 percent alcohol content was pushed on us in the last couple of years. My car ran fairly well when it was 10 percent but when the 15 percent was approved it began acting up even though I was buying supposedly 10 percent premium. Fortunately, a new station was built locally that has no alcohol premium and regular grades. My drivability issues disappeared when I started putting the no alcohol content premium in the tank. Drivability issues return when I have to buy the alcohol laced fuel that's supposed to be 10 percent.
I'd check the exhaust with an exhaust gas analyzer and see if it's running too rich.
One of the things that ethanol does is co-evaporate with some of the mid distillate and if the car is hot, and the fuel is "boiling" then too much fuel might be getting in and it won't burn above the UEL. When it cools down, it's "ok" makes me think this.
May have to rejet for ethanol also. They do for racing. If you have the original jets for the old gas, they may not be right/best. Since new needles helped, it might be part of the issue.
They slop a lot of gas around the world now, so it could be a water content issue too, but speculating. Since cars are mostly injected now(closed system), this doesn't occur with them.
This was one of the poorest decisions the EPA/Govt ever proposed, in my opinion. And to subsidize it was an assault on our treasury. Of course, they can care less about our "clunkers".
ps: most of these era cars because of their higher compression ratio call for premium fuel, 93 octane, so don't pull up to the regular 87 or 89 ethanol hoses.
Unfortunately out here in California there's only 91 Octane and zero options for non ethanol stations.
That is true that our engines are high compression and need the highest octane available to run smoothly.
On my 54 because the 331 is only 8:1 compression ratio so the engine doesn't need such high octane to run smooth, so 91 seems ok for it, but my 64 with the 429 and 10:5:1 ratio, it obviously needs around 100 octane to operate the best and the ethanol does make it more difficult for our cars to run without rejetting the carbs to allow for a richer mixture.
This is why all of my cars that have its original carburetor, I need to richen up the idle mixture screws and can't go based off the shop manual anymore, and this goes for my Lincoln's as well with a 2 barrel Motorcraft carb and a 400 CI engine.
Modern fuel sucks.
Gasoline is shipped from the refineries in only 2 octane ratings. The regular grade is 84 and the premium is 90. The Deathanol is blended into the fuel at the transport tanker loading facility to create the desired blend. Specialty blends are created by adding other additives after the fact.