purpleomega

So I went looking around the forums, but didn't find a definitive answer to a problem I'm having. When I start my '82 Carbureted V6, it runs rough, my options on a cold night are A. Hold the gas down for a few minutes to let her warm up and then drive away. B. Rev it once really quick and get her in gear before it stalls. C. Turn my defroster on high. If I don't do any of those, my car will pretty much stall, but upon restarting, it sometimes runs better immediately. The first thing I tried was the Choke Thermostat, but that didn't help anything. The closest I've found in the forums was to change the Coolant Temperature Sensor. Does anyone out there think that might be the answer, or should I be looking for something else?

Air_Adam

Coolant temp sensor won't fix anything, because even if its electronically controlled like some 4bbl 305s were, the ECM ignores most sensors untill it hits about 40*C (about 90-100*F) or so.

When its stone cold, snap the throttle open and see how far the choke plate closes - should have a gap somewhere between 1/8" to 1/4" to the choke horn. More, and it will be too lean and will cause a rough idle and stalling, but will clean up as the engine warms up.

You should also check the fast idle speed setting - for some reason, lots of people try to adjust it WAY down, so it can idle at almost a normal idle speed when its stone cold, like an EFI engine does. You can't do that with a carb, and you get problems like this as well. It should be set to immediately make the engine idle around 1200-1400 when first started, and that will climb slightly (1600 or so) as it warms up and the choke opens, untill you kick the throttle and it will drop it down to a normal idle speed.

purpleomega

OK, I adjusted the fast idle screw and it worked.....until I pushed on the accelerator cable. It cooled down and worked again once, but when it sat for hours and was really cold, it was the same as before. The cam doesn't want to stay behind the screw, any ideas?

Air_Adam

What do you mean 'wont stay behind the screw'?

purpleomega

OK, this is a diagram I found online and not Camaro or GM specific, but it will get the idea across. I set the cam to the highest position, tightened the screw and it idles high. As soon as I pull the throttle cable, the screw pulls off the cam, the cam snaps up and it idles normal. I think the problem I am having is whn the car is cold, the cam won't sit on the screw the right way. I'm not very good with carbs, so if I'm an idiot her, just tell me, I won 't be offended!

Air_Adam

It is supposed to do that, if I am understanding what you are saying correctly. When you tap the throttle, it should drop down to a lower rpm, something at or close to normal idle speed. You have to let it warm up a little longer before you hit the throttle.

purpleomega

Yes, but when it gets cold again, it doesn't idle high again.

Air_Adam

Do you pump the gas a few times before you try to start it? You need to do that to set the choke, and the fast idle should engage at the same time.

purpleomega

Yeah, usually at least one big pump.

purpleomega

Tried pumping more and no difference? Any takers?

purpleomega

I got nothing, does anyone have any ideas?? It's still somewhat warm up here, but it's getting to that time of year where I need this car to run on it's own. Please help!!

89IROCZ28

iTrader: (14)

When the engine is cold, take off the air cleaner and observe what the choke and fast idle cam does when you do the following:

Before starting the engine:
- Press on the accelerator one time. Not fast, just one smooth action.
- This should close the choke and set the fast idle screw on the highest point of the fast idle cam.
Note: If you step on the accelerator too fast or more than once, you may force the choke open & 'kick down' the fast idle cam. You also will be pumping more fuel into the manifold w/ each additional press of the pedal.
- If the choke isn't closed or very close to it, adjust the choke thermostat until it just closes. You may have to adjust it a little one way or another depending on how rich or lean it runs once the engine is started in the next step.
- Also, if the fast idle screw isn't on the highest step of the fast idle cam, either slightly bend the linkage connecting the cam to the choke plate or adjust the choke thermostat. Which one depends on how rich the engine runs once it's started.

Start the engine ...
- The choke should open slightly, 1/8" - 1/4" depending on the temperature.
- The engine should run fast, but smoothly.
- If the engine is running rough, determine if it's running too rich (black smoke out the exhaust) or too lean. If it's running rich, adjust the choke thermostat so the choke opens just enough to make it run smooth. Adjust the thermostat in the opposite direction if you suspect it's too lean.
- Adjust the fast idle screw for an rpm between 1500-1800 while it's on the highest step of the fast idle cam.
Note: You'll have to work fast to make any of these adjustments before the engine warms up too much. If the choke thermostat warms up too much, you'll have to wait for everything to cool down before trying to make any further adjustments.

As the engine warms up:
- The choke should be opening very slowly (almost too slow to notice) and the engine idle will probably increase, too.
- Tapping the throttle should cause the choke to jump open a little and the fast idle cam to drop a step or two, lowering the fast idle speed.
- If the engine is warm enough, tapping the throttle will also cause the choke to open fully (if it's not already) and the fast idle screw to drop off the cam completely, letting the main idle adjustment screw control the rpm.

Hope this helps and doesn't make it more confusing.

purpleomega

So I took the air cleaner off and had someone step on the pedal for me so I could watch what was happening. The fast idle cam did drop, but only to the second position. The first time I watched it, the car actually did idle higher, but that was the only time. I tried to adjust the choke thermostat (again) and got nothing. I did not want to bend anything, mainly because I didn't know what I should bend or if it would actually do anything......nothing seems to be working. It seems like when I have the air cleaner off and screw around with it, I get some improvement, but once it's back on, it's the same as before. What could cause this?

89IROCZ28

iTrader: (14)

Did/does the choke close all the way when the engine was cold and the throttle pressed one time? Does the choke open at all once the engine is started?

Is the air filter new or dirty? A dirty air filter will restrict airflow and create a richer mixture.

purpleomega

I think the choke is doing what it's suppose to do? If I remember correctly, it closed and then opened slightly when I started the car. The air filter is a little dirty now, but this was going on when I bought the car in back March, and I have replaced the filter since then.
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I remember when I bought the car, the induction side of the air cleaner was full of debris and chestnuts.

89IROCZ28

iTrader: (14)

Try adjusting the choke so that it's open a little more, another 1/8" or so. Does it run better or worse?

If you can't detect a difference, what happens if you open the choke all the way? Does it run better, stall out, or still no change?

purpleomega

When I adjusted the choke thermostat, I set it to open a little more. It just stalled right out.

89IROCZ28

iTrader: (14)

That sounds like you're not getting enough fuel. If you adjust the choke to stay closed longer does run better or also stall out? If it stalls, pump the throttle by hand a couple times. Do you get a shot of fuel down the carb from the accelerator pump each time? If not, you're definitely not getting enough fuel. Check fuel pressure, filter & pump. It could also be the pickup in the fuel tank.

89IROCZ28

iTrader: (14)

Just re-reading your original post ... does it still run well after warming up?

purpleomega

Runs like a dream after it's warm. The only other thing I can think of that might effect it, is a small exhaust leak on the passenger side manifold that also goes away when the car warms up. I don't think it has anything to do with it because all off the choke stuff is on the driver's side manifold.

89IROCZ28

iTrader: (14)

In that case it's not likely to be the fuel pump. I'd concentrate on choke & fast idle adjustments.

Is there a heat riser on the V6? Is it stuck open?

purpleomega

Is that the flap on the air cleaner? If so, yes, but I don't think it's stuck. When I bought the car, I cleaned it out pretty thoroughly, I think a rodent might have gotten in it because there were a lot of nuts and debris. I remember making sure that it was opening and closing easily.

89IROCZ28

iTrader: (14)

No, it's on one of the exhaust manifolds - usually right before the connection to the exhaust y-pipe. The valve is inside the manifold, so you won't be able to see the actual valve plate. I'm just not positive the carbureted V6 has one. If it does there should be a round weight and spring. With the engine cold, you should be able to rotate the valve by hand and it should spring back - if it's not stuck open.

When working properly it'll be closed when cold, causing hot exhaust gases to be forced through a passage in the intake manifold which helps keep the fuel atomized while the manifold is cold. Similar to a choke, the bi-metal spring controls the position of the heat riser valve. When the exhaust manifold and spring heat up, the heat riser valve opens. It's common for the spring to break or for someone to wire the valve open - or even remove it - because it rattles or isn't opening all the way. This may cause poor performance while the engine is cold.

But, the carburetor choke should have a greater effect on how the engine runs when it's first started cold. So, I'd adjust the choke to stay closed longer (richer) in small steps to see if it starts running better. If you go too far, you'll get a lot of back smoke / carbon out of the exhaust. As someone else already mentioned, you may also need to adjust the fast idle screw to increase the engine speed until the choke is fully opened. I don't know what the spec is, but shoot for 1500-1800 rpm. The actual spec may be higher.

purpleomega

I will check my chilton's tonight and see if there is a heat riser. That makes some sense because sometimes when I start the car, I hear and feel a weird vibration from right about under my feet in the exhaust and it'll puff out a pretty big white cloud of smoke. As with everything else, it's fine when the car is warm.