Help! Dies At Idle In The Cold

[2B32]

I have a 71 w/350 and Edelbrock 1406 carb. It idled fine in the summer, but now that it's cold it dies at idle. It runs fine as long as I keep my foot on the gas, but sputters and dies as soon as I let off. I checked the choke and it's fully closed. Also, the vacuum line from the distributor is plugged into the timed vacuum port for emission controlled vehicles. Should it be plugged into the vacuum port for non-emission controlled vehicles?

How do I fix this? This is my first experience with a carb, so pardon my ignorance.

[HO455]

Your choke shouldn't be fully closed. I don't believe those carbs have a choke pull off like a Q-Jet so the flapper should have some gap before starting. About a 1/8" or slightly less gap on the edge of the choke flapper. The primary throttle blades should also be slightly open on the fast idle can. If you have a tach shoot for 1200 RPM when warmed up on the cam. I'm pretty sure you can find a copy of the owners manual on line with the exact specs.
Your vacuum advance should be plugged into the ported vacuum supply. This will prevent the vacuum advance from affecting your idle

[i82much]

carb may be icing up. do you have a heat riser valve in the exhaust and/or a thermac air cleaner?

[geezer#99]

If your choke is fully closed then it shouldn't run.
Otherwise it just sounds like a cold intake plenum due to no heat.
Do you have headers?
What intake manifold?

[2B32]

So, it turns out I didn't have a power wire connected to the carb. I fixed that issue and it seemed to be running and idling fine. It started and idled fine this morning, drove it to work, but this afternoon it started dying under idle again. I did notice the choke is not closing with the first press of the pedal this afternoon. What's wrong now?

[davepl]

Got to disagree with Geezer on this one. The choke should be FULLY closed before starting, and as soon as the engine fires, the choke pulloff diaphragm will then open the choke blade to a specified amount, where it needs to be in order to run.

But before starting it is indeed fully closed.

To run "well" in actual cold (like well below freezing) you'd ideally want the heat crossover working and the heat stove, and especially the ThermAC valve on the snorkel... without that it'll bog on any rapid throttle application until it's very fully warmed up. Properly tuned and adjusted a Q-Jet in the winter is close to EFI, but my true favorite is the 2GV, which is unstoppable in the cold weather.

[2B32]

Originally Posted by davepl

The choke should be FULLY closed before starting, and as soon as the engine fires, the choke pulloff diaphragm will then open the choke blade to a specified amount, where it needs to be in order to run.

That's the way I had it set on Saturday, and it was working as it should this morning. But, for some reason, now the choke wont close with the first push of the pedal. What could be causing that all of a sudden? The temps were 35-40 this afternoon, so it wasn't terribly cold.

[geezer#99]

Just loosen the cap again and rotate a bit richer. You likely have it set too lean.

[HO455]

My experience is that setting up a choke involves three operations. First make sure that the flapper goes all the way closed when the engine is dead cold. You want it to be fully closed but just barely. This must be set after the throttle has been depressed once to set the throttle on the fast idle cam. Once that is done start the engine and check the choke pull off distance. This setting allows the engine to get the correct amount of air to run. These two adjustments must be done on a cold engine. For me this means drive to work and checking it before I go home. It usually take 3-4 days making one adjustment at a time before it's correct. The third one is to make sure the flapper is fully open when the engine is hot. I this check once I get home. The heat crossover is to prevent carburetor icing in cold weather and has no affect on the engine starting and idling when cold. Its other function is to keep the bottom of the intake hot to prevent fuel from puddling. Any raw fuel that makes it to the intake floor is quickly evaporated.

[davepl]

You want it to be fully closed but just barely.

Depends on the temp. If it's 50F, then you probably want it just barely closed. But if, like in my misspent youth, you're standing on an orange crate in your frozen dirt driveway adjusting it in -40F weather, then it needs to be fairly tight I'd imagine.

Honestly if it were me I'd set the choke tightly closed, fire it up, and let the choke pulloff work which pulls it open a small bit. As it then warms up it'll get to a point where it wants/needs more airflow than that small gap, and once it comes obvious that it is being "choked", I'd rotate the choke adjustment to open it to the highest idle speed, which will be just a touch more open. From there it'll proceed to open to full at operating temp on its own. That'll get you very close.

[demian5]

Sounds like you need to have someone that can adjust the carb come and do that. Its an art.