So, where did that tube run originally? I'm also missing the tube between the exhaust manifold and the intake. How important are these, really?

 

The small tube went to the exhaust manifold, and was fed from the small rubber hose that comes off the top, just under the air cleaner.
The larger tube that runs from the exhuast manifold up the air cleaner inlet snout just allows the engine to draw warmer air during warmup, in cold weather. I don't guess it's super important, as my truck has been missing that for more than 13 years. I was going to put one on, till I noticed the part it attaches to on the exhaust is gone........

 

Just tried to start the truck after 2 days sitting, and it fired right up. Great big thanks to you all!

 

Glad you got it figured out!

Rogue_Wulff is right; you need to eventually get your automatic choke system hooked up or else you are going to hate your truck when the weather turns cold! The insulated metal line you speak of that is attached to the choke cap is a very important function on carbureted vehicles. Right now it is broken off and open, which means you have a vacuum leak. This is part of the automatic "hot air" choke which a carbureted vehicle absolutely needs!

When the engine is cold, it needs a richer mixture to stay running, and that is why the choke closes. Clean, filtered air from the air cleaner is pulled through the "fresh air" tube (red hose in your pictures that should attach to another metal tube) and into the top of the choke stove in the exhaust manifold, where the air is heated up when the engine is running. From there, the heated air goes back up through the insulated "hot air" tube (attached on the bottom of the choke stove on the exhaust manifold) that attaches to the choke cap. As the air gets hot, it closes the spring in the choke cap, which allows the choke plate to open up as the engine warms up to run on a leaner mixture.

When this is hooked up correctly, you will have quick cold starts and much better driveability. With the proper carburetor settings and the "hot air" choke hooked up, you will find that a carbureted engine can run just as well as any modern fuel injected vehicle. Last winter, after I got my own hot air choke hooked back up, it got down to 10 degrees here (that is COLD in SC) and my truck started right up with only one single pump of the accelerator pedal and it never stalled!

The larger tube that connects from the exhaust manifold to the bottom of the air cleaner snorkel is part of the "thermostatic" air cleaner, and it works in much the same way as the "hot air choke" system I explained above. There is a small motor located right on top of the air cleaner snorkel that senses the underhood air temperature. When the air is cold, a flap closes in the air cleaner snorkel, which closes off cooler outside air from coming in through the cold air tube that attaches to the radiator support. When this flap is closed, heated air is directed from the exhaust manifold and into the air cleaner to keep the carburetor from icing up on cold and humid days. Likewise, when temperatures are warm enough, the flap opens up (default position) and only allows cool, outside air into the air cleaner, which helps performance.

So Ford actually supplied these vehicles with a stock "cold air intake" that people pay good money to get now! For some reason, most people like to throw these away and replace it with an aftermarket chrome air cleaner, which does nothing except sit there and look shiny, while supplying your engine with hot underhood air, which actually hurts performance.

Unless you live in a very cold area, all the factory air cleaner connections are not absolutely necessary, but they do have their advantages. The "thermostatic" air cleaner really is a useful system, and I plan on getting mine hooked back up soon.

 

Thanks for the very through explanation. Can I buy a replacement tube somewhere, or do I ave to buy tubing and bend it myself? The larger tube is a straight shot, I assume I can find something at the parts store for that. Can you tell me exactly where the hot air tube connects on the other end? I poked around briefly, but didn't see anything obvious.

 

The "hot air" tube connects from the choke cap to the exhaust manifold. Follow the "fresh air" tube and you will see it connects to the top of a little chamber (also called a choke stove) on the side of the exhaust manifold. At the bottom of this chamber is where the insulated "hot air" tube should be attached.

You can special order choke stove replacement kits from NAPA or CarQuest, and they will come with a replacement tube (you can bend it to shape by hand) and insulation. Or you can use brake line to replace your broken "hot air" tube, but be sure to transfer the insulation to the new tube.

You can buy the larger exhaust manifold tubing from NAPA, part number is BK 8191129, duct hose.

Store Locator | NAPA Online

The air cleaner "cold air" tubing is part number BK 8256031, air cleaner inlet hose.

Store Locator | NAPA Online

 

Ah yes, I see Advance Auto has a universal kit for like $7 Sounds like a project for next weekend. Rather do it now before it gets cold. Is it likely I'll have to adjust the choke spring when it gets cold anyway, or this should be a 'set it and forget it' type deal?

 

Depending on the area, some people set the choke cap at one setting in the winter, and another in the summer. It is usually only a click or two difference though. I set mine last winter two clicks leaner past the center, and it seems to work well there year round.

 

Excellent, thanks again. You've been very helpful.

 

Glad I could help!

 

2 lean is the same setting I use, and is the setting that I generally suggest starting at. I'm not sure, but I believe the factory service manual calls for 2 lean in all but the coldest areas.

 

Ok, back to the drawing board I'm afraid. After I fixed the choke, I let the truck sit for 2 days, and it fired right up when i tried to start it. Last night I went to use it after sitting for over a week. I stepped on the gas to set the choke, turned the key and it just cranked like it did before. I cranked for 10-15 seconds, let it sit for a minute, did it again and finally resorted to the old gas down the carb trick. So, I guess the real question is, what's different between when I try to start it a day or two after using it, and a week or so after using it?

 

Since we are talking about the Carter YF, here is one possibility. The YF uses the accelerator pump diaphragm for two purposes: 1) to pump fuel to the accelerator pump nozzle. 2) as a vacuum diaphragm to control the moving mixture needle in the main jet. The top of the diaphragm is exposed to the fuel in the bottom of the fuel bowl. The bottom of the diaphragm is connected to manifold vacuum. If the diaphragm has a SLIGHT leak, you won't notice it in terms of performance. When the truck sits for an extended period, a small leak can allow your fuel bowl to drain into the manifold. If you have a serious leak, you will find that the engine runs really rich, shakes and coughs, won't idle, and generally runs like crap except at WOT.

You may have a small leak of the pump diaphragm. The solution could be as simple as taking the top off the carb and tightening the 4 screws on the pump diaphragm cover. Worst case is a carb rebuild to replace the diaphragm.

I have had to rebuild my YF 2 times in the last 3 years just to replace the pump diaphragm. They do not hold up well to modern fuel with ethanol. I suspect the rebuild kits are probably NOS from the 80's or 90's.

I am getting ready to remove my YF and replace it with another type of carb. The best thing to do with a Carter YF carb is give it to somebody who you don't like.

 

Is there a way to check the diaphragm? The car bwas rebuilt by a reputable shop right before i bought the truck a few months ago. I saw the itemized service receipt.

 

if you let it sit a couple of days *before you do anything* take the lid off the bowl and see if it is full of fuel.

Like I mentioned in post #4..