For about a year I've an annoying issue with the roadster. The '52 DeSoto Hemi has an (increasingly occurring) stumble accelerating right off idle. It seemed that it's a "too-lean" issue, and I had tried to overcome it by enriching the choke setting. (I know, I know, that isn't the "right" way, but I figured it was worth a try, right?) This morning I let the car idle in the driveway for a few minutes while I did something, when I walked behind the car my new, brushed concrete drive was stained with black carbon from the exhaust. Crap. So, I thought about the problem for a minute while I drove to the grocery store, increasingly annoyed with it stumbling and coughing, figuring that a 4 year diet of 15% ethanol regular might have something to do with this increasingly noticeable problem. When I got home I looked on-line for a carb kit for the obsolete, 2 year only Carter carb. Guess what? Two clicks got me to a supplier, and $95 later on my debit card I have a rebuild kit coming for it. I'll have it in a few days, and will be anxious to see if my diagnosis is correct and I can dial the choke back to where it's not flooding to overcome this.
Check the ignition while you are at it. These cars and engines required regular maintenance, and the parts available these days cause a lot of threads on top of that. Best of luck getting it back into tip top shape.
Brian - 1. Where is your ignition timing ? If..."per the book"... Increase ignition timing 4° then try 6° . 2. Open both of the idle mixture screws from smooth idle by 1/4 to 1/3 a turn more. 3. Hard to tell...put the accelerator pump arm in the first (shortest length) hole). Mike
I can play with the timing a little. I advanced until it kicked back against the starter when warm, then just backed it off a little until it no longer did, so I don't know if there's much left to advance without causing more problems. And, moving the pump am was my first thought, but there's no adjustment on this particular carb. So, I'm going with the pump may be the issue. Thanks for the thought on the issue.
Set your timing to spec [vacuum advance disconnected] then re-connect the vacuum and take anothe reading of the timing with the light [it should pull another 4°- 8° with the vacuum at idle] Then disconnect the vacuum and advance the timing so it is the same at idle as before [with the vacuum connected] Connect the vacuum to ported vacuum. [or simply try it without vacuum advance] I have had a lot of off idle stumble issues fixed by going to ported vacuum [this is because you usually get max vacuum at idle, and zero vacuum when you open the throttle] The advance can instantly drop from eg: 14° - 16° back to 8° - 10° when you touch the gas pedal causing a stumble. Try it ..... It doesn't cost anything
This type of problem is often a bad diaphragm or cup in the accelerator pump and the ethanol mix gas attacks rubber even faster. If it was a modern carb they make accelerator pump replacements that are designed for this crap gas, but yours being an old carb will likely require you to rebuild it every so often until the carb gets replaced with something modern that accepts the modern accelerator pump diaphragm.
You need the accelerator pump squirt right at the crack of the throttle. Holleys are the easiest to set.
I’d have to lean toward the carb. Probably the accelerator pump. Gas these days is terrible. Basically rots the rubber in the older carbs
I never use ethanol gas in my older cars and we have a house in Florida and non-ethanol gas is widely available there because of boats/golf carts etc........
Yeah but you've been running it with the choke partly on. I think it's worth pulling a plug or two to make sure they're not all black and fuzzy. I honestly don't think it's the plugs, because usually if the plugs are fouled, it'll idle but won't rev up. But at least you'll know for sure.
Have you considered changing to a 'newer' carb? Plenty of big 2bbl from early 70's. Carb kits will be cheaper and easier to get a better accel pump.
are you running a stock mechanical fuel pump? or electric? If you are running an electric pump, does the PSI does it match with the carb?
I know about 2 bbl. to 4 bbl. adapters. They're the automotive equivalent of shoving a cucumber down the front of your pants.
I primarily run Rec-gas (non-ethanol) in it down here, but it's mostly been fueled with regular with ethanol. In Michigan, where it's been up until now, when stored I disconnect the fuel line at the tank and run it until it's out of fuel so as to not let the fuel pump and carb set 4 or 5 months with ethanol fuel in 'em. Honestly I don't think that's much of an issue, as carbs needed to be rebuilt and fuel pumps replaced regularly "back in the day".
Hot Heads offers a 4 bbl intake for these low-deck DeSotos, but it's UGLY. I had gotten a 2-4 bbl adaptor for it back in Michigan to put a new E carb I have on it, but the base of manifold is wildly different than any other 2bbl base those things will bolt up to. So, I'm kinda stuck.
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