I had something similar to this happening a couple years ago on my '73. Whenever I tried to go up any sort of incline, my truck would bog and eventually die. After rebuilding the carb twice and still having it happen, we eventually found the cause to be a pinched fuel line. I'd suggest testing your fuel pressure and seeing if the pressure dips when cold and comes back after everything is warmed over.

 

Small update.

First off, after reading some more on carb icing, I can see why you were talking about the cold weather pre-heating on the intake.

I thought you were mentioning it with the idea that the cold air is just making it drive poorly, which I know is can, but I knew that's not what this was. I definitely know what the symptoms of ice cold air on an ice cold engine are. I just shrug those off and deal with them until the engine warms up.

However, warm air going down the throat of the carb is also essential in preventing carb icing, which I wasn't getting from your guys' context. In that regard, I can see why it's definitely important for the winter.

So, thanks for the ideas on that.



On that note, though, my engine started acting up again this morning, so I pulled over in a parking lot so I could quickly look at it. It struggled, but continued to idle around 200 RPMs with an AFR of around 10:1. I popped the hood and pulled off the air cleaner.
The choke was 100% fully open, so it's not the issue.
I then turned the engine off and opened the throttle blades to WOT and looked down the venturis with a flashlight. They were clean and open with no signs of icing of any kind. Not even any frost. Everything looked completely normal.

It fired right back up, (but still stumbled and struggled) and I went on my way. After a few minutes, it went back to behaving like normal and drove great.

So, I don't think icing is the issue unless I'm missing something.

 

As for fuel pressure, a fuel pressure gauge is still something that I haven't installed...

What would fuel pressure do to cause this? I don't seem to be lacking for fuel by any means.

 

Kinda like a light bulb will sometimes flicker (sometimes for a while) before it burns out?

 

i don't know how serviceable the DUI distributors are...but they're an HEI derivative. I've had very similar intermittent issues with a bad coil. that would explain a lot. hope it works out for ya AB.

 

The DUI is simply a beefed up HEI that's tailored to fit different engines. So, parts are interchangeable. I'll do a test on the coil to see if anything's out of sorts.
As for the on/off nature, it doesn't really go back and forth. It's generally starts in about 20 - 30 seconds after first firing up, and then will go away after 10 - 15 minutes of driving (about 5 - 10 minutes after the temp gauge has reached operating temperature). And it's invariably after it returns to idle (like at a stoplight).

One thing I did notice this morning, back on the carb icing thing, is that the transition slots were filled with frost. Could this be the cause?

 

IMHO, scrap the auto choke and convert it to a cable actuated manual if you can't get it adjusted properly.

 

As far as I can tell, the choke seems to be working perfectly.

 

Justin - are you asking if it's maybe a temperature-dependent problem?

 

I'm about 99% sure it's temperature related.
I had the same issue last winter.

I just can't track down what it is.

 

This is still for your 1981? Probably 6-banger?

 

That's the one.

 

The pump may be supplying too much pressure that will "blow the needle off the seat" causing overly rich. It may also be that your float is partially collapsed or "water logged", or the float level may be too high. Also, check to make sure the bowl is properly vented, either through the charcoal canister system if installed or through a bowl vent.

 

Is the fuel pump something that could be affected by the cold? I only have the issue when it's below freezing out and once the engine warms up, the issue goes away. But it's persisted through two carbs, so probably not the float .

 

Check the fuel pressure to be sure