Cold engine stalling after acceleration

[RudeDog]

Howdy All -

I have a 78 with an engine stalling problem. After starting the engine cold and driving for a short distance (before the engine has been allowed to come completely to temperature) the engine will stall when I let off the gas to stop for a stoplight. The engine easily re-starts but will sputter a bit when I try to accelerate once again. Then it will run fine until the next stop. This will continue until the engine comes up to normal operating temp at which it will run very well. I've checked that the automatic choke is operating properly and it appears to be fine. I think I'm able to repeat the problem by just starting the engine cold and slowly accelerating the engine in neutral and then letting it return to idle quickly but I'll need to confirm that tomorrow (I thought of trying this after the engine was pretty well up to temp and I haven't had a chance to try it again since its cooled back down). I'll be digging into the problem more tomorrow by doing the following:

1 - check for any leaks around the base of the carb or any air lines to/from the carb.
2 - start looking into distributor condition / gap / dwell / timing.

Any suggestions?

Thanks,
Rudy

[So Cal Mark]

even though the choke appears to operate, how is the fast idle speed? There is a separate adjustment for that.

[RudeDog]

Help me out on that one. By "fast idle speed adjustment" are you referring to the screw that sets the idle speed for the choke that releases in small stages as the choke plate rotates open? I think that idle is set correctly. However, I've seen some other posts that deal with the emissions equipment and refer to it as something to do with fast idle... I'm more foggy on that. Are there any strings that explain how to adjust what you're talking about?

[So Cal Mark]

that is the fast idle screw I'm describing, it contacts the steps on the fast idle cam of the choke. There are specs for choke opening and fast idle speed

[RudeDog]

I think I might have figured it out (but I'll have to take a test run after the engine cools off to prove it). I was working on making adjustments to the fast idle adjustment screw on the choke and then started looking at the distributor when I noticed an air leak sound. It turns out that the metal tube connecting the EGR valve to the intake manifold was cracked allowing cold air into the intake manifold rather than warm air from the exhaust manifold. I'm guessing that since we've had really cold weather here lately, that the air leak was primarily cold air until the engine compartment was warmed up enough that the air coming in from the leak and the air coming from the exhaust manifold were pretty much the same temperature so that the carburetor really didn't know the difference. At that point the engine would start running normally. Plugging up the leak (with some Liquid Steel) made an immediate improvement in the sound of the idle (smoothed it out). If this ends up being the fix for the cold engine stalling problem then it ended up being a very providential find and simple fix.

I've got it sitting out in the snow to cool off for a test run later.

[RudeDog]

That was the problem. It hasn't run this well since I got it a couple months ago. Now I can move on to some of the more cosmetic things.

[mdrburchette]

Great to hear you found the problem. Wish my repairs went that well!

[So Cal Mark]

it's not a cold air/hot air thing, it's a vacuum leak

[RudeDog]

I was trying to account for why the problem went away (or at least was much less of a problem) once the engine was at normal operating temp.