02Pilot
02Pilot Dork
8/22/18 3:03 p.m.

Just looked over a buddy's 1946 Chrysler. He's trying to sort out some running issues, and looking things over I came up with a few questions. Since I figure the hive has to know something about these, here we go.

- It's a C-39 straight 8 with a Carter 1-barrel carb. The carb needs to be rebuilt, but looking at the manifold I suspected that a 2-barrel option must have existed, as there is what looks like a 1-to-2 adapter between the carb and manifold flange. Sure enough, this motor also came with a Stromberg AAVS-2 2-barrel. To me this seems a natural upgrade path, since the old carb has to come off anyway. Any reason we should not be looking for a 2-barrel to bolt on here? Will it bolt on the manifold, or is another spacer/adapter necessary? Are the linkages the same?

- Right now, the car starts and idles fine, but when you open the throttle past about a third, it bucks and coughs. There is a smell of unburned fuel when it does this. Plugs and wires are new, as are the points, condenser, cap, and rotor. A new coil is on order. Aside from the usual further troubleshooting (we need to look at the oil bath air filter and the fuel system), any issues specific to this engine we should be aware of?

There may be more questions in due course, but that's enough for starters.

Dusterbd13
Dusterbd13 MegaDork
8/22/18 3:17 p.m.

Check the mechanical and vacuum advance on this distributor 

In the 60s through 80s, part of an oil change on mopar was adding a few drops of oil to the oil wick under the rotor button. This kept all the advances moving freely. I would ASSUME that this has been neglected for about 30 years, just like the older vintage mopars, and as a result the advances are locked up solid, or very stocky/notchy in movement.

pirate
pirate Reader
8/22/18 3:34 p.m.

Carburetor float sticking? Float adjustment? 

noddaz
noddaz SuperDork
8/22/18 3:52 p.m.

Check the distributor advance like Dusterbd13 said and also check the accelerator pump in the carb.  The plunger/diaphragm might be dried out so it does not pump fuel.

 

noddaz

02Pilot
02Pilot Dork
8/22/18 3:56 p.m.

I suggested he check the distributor advance when we talked about it a week ago, but I forgot to ask if he had. The carb is weeping fuel everywhere, so I wouldn't be surprised if it's part of the problem too. The car had been running fine for two years, so it's not simply a case of stuff rusted together for decades.

Vigo
Vigo UltimaDork
8/22/18 10:47 p.m.

I think my first priority would be to do an actual test to see if it's actually lean or rich during the misbehaviour. It takes a whole lot of fuel to make an engine choke up, something like 2-3X the 'proper' amount. In a carb there's not much that can make or allow it to flow 2-3x what it's supposed to aside from a stuck-open float valve, and that one isn't throttle dependent so i dont think it applies here. I suspect it is actually lean.

aircooled
aircooled MegaDork
8/22/18 10:55 p.m.

Are you saying opening the throttle while sitting, not moving?

if so, I would say a clogged transitional circuit in the carb (one of those little passages in there).  Possibly the main circuit (main jet).

Not sure it will work with the transistional circuit, but a clogged idle circuit can sometimes be cleaned by blocking off the carb with your hand while it is running (creating a lot of vacuum)

 

Trans_Maro
Trans_Maro PowerDork
8/22/18 10:59 p.m.

Are the points gapped properly?

Single or dual points? The setting is different for both.

I just spent time with a 1931 Packard that someone had converted to single points but had used the larger gap setting for the dual points on the single point set resulting in very poor running once the RPM came up a bit.

As for the carburetor, if he's interested in originality, go to the original carb. If not, a more modern 2-barrel might be the ticket.

A lot of those earlier carbs are die cast pot metal and have started returning to the earth as their grain structure breaks down. They're a good way to start an engine fire.

02Pilot
02Pilot Dork
8/23/18 7:43 a.m.

I don't think originality is a big priority - he's not planning to sell or show the car, just drive it.

I will see if I have time to get over there tomorrow and look at the distributor. From what I can see the question of single or dual points isn't an issue until the early 1950s cars, but I'll double-check.

If the carb body itself, rather than just the gaskets, is seeping, what are the alternatives? Is there anything more modern that fits without major modifications?

Trans_Maro
Trans_Maro PowerDork
8/23/18 11:44 p.m.

Dual points were used very frequently on straight 8 engines in the 1930s, it might have them.

As for the carburetor. I can't give you an exact interchange, you'd have to measure the bolt hole locations and find something.

The nice thing about carburetors is that they meter fuel by airflow so a carburetor form a later engine of similar displacement will be jetted pretty correctly for your application. I would be looking pretty hard at Rochester 2G carburetors and Weber DGAS series.

02Pilot
02Pilot Dork
8/24/18 8:27 p.m.

Single points setup. He's got the factory workshop manual and set the gap by that, so hopefully it's right.

We talked about the possibilities and we came to the conclusion that the first thing to look at is the choke. He said another friend of his was messing with it at some point and he thinks it may not be right. We shall see.

Dr. Hess
Dr. Hess MegaDork
8/24/18 8:58 p.m.

Sounds too lean to me also.  Probably gunked up jet or bad vacuum leak.

JamesMcD
JamesMcD SuperDork
8/25/18 9:02 a.m.

Can we get a picture? I love this body style.

02Pilot
02Pilot Dork
8/25/18 9:26 a.m.
JamesMcD said:

Can we get a picture? I love this body style.

It's pretty tightly packed into his garage right now, but the next time it's outside I'll grab a shot or two. The paint is tired, so it's hardly a show car, but it's remarkably solid and pretty complete.

Trans_Maro
Trans_Maro PowerDork
8/25/18 9:41 a.m.

Honestly, if you're questioning the fueling at all and if it's been sitting a while, it's best to dismantle the carb and give it a good cleaning.

If it's a 1-bbl, it's probably a W1 and very simple to work on. The kits are cheap.

The accelerator pump is probably shot from sitting. If the new one is leather, soak it in oil for a little while before installing. If it's blue rubber, it's ready to go as-is.

Use a strand of copper wire to poke through all the little passages and the straw on the carb cleaner can to blow through and make sure they're clear.

Ideally, I'd soak it overnight in a dunk type cleaner like Gunk Hydroseal II

02Pilot
02Pilot Dork
8/25/18 6:57 p.m.

It's a Carter BB carb. Looks quite simple - I found some good tuning instructions. Depending on his timeframe and mine, I may suggest he let me rebuild it over the winter. I'm going to do the Weber DCOEs from my 2002 anyway, so I'll have the dunk cleaner and brushes and probes out anyway.

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