Removed carb to rebuild as part of performance trouble shooting and found the tube running from the exhaust manifold to electric choke on the carb broken at manifold. It appears to have been broken for some time. Anybody know what this tube is called and what it's for?

 

If you mean the metal line with the insulating jacket, it supplied hot air to the choke housing to facilitate the opening of the choke.

This link might help: https://www.ford-trucks.com/forums/1...ent-101-a.html

 

The tube with the frayed insulation on it is the hot air choke tube, and it is very important.

As it is now, your choke is not working good, if at all. I bet you are having a hard time starting your truck when it is cold outside. When these trucks have the choke system hooked up correctly and functional, the engine should start right up with a single pump of the gas AND CONTINUE RUNNING WITHOUT PATTING THE GAS OR STALLING, no matter how cold it is outside. Wouldn't that be nice?

A thermostatic "hot air" choke in conjunction with an electric assist is what Ford used on the stock Carter 1V carburetor and Motorcraft 2V carburetor. The way it works is this:

I. Thermostatic "hot air" choke
Clean, filtered air from the air cleaner is pulled through the "fresh air" tube (the red rubber hose that is connected to the carburetor air horn and fits over an aluminum tube) and into the bottom of the choke stove chamber on 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 top of the choke stove chamber on the exhaust manifold) that connects to the choke cap. As the air gets hot, it relaxes 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.



If your original choke tubes have rusted off, you are going to have to remove the exhaust manifold from the engine and drill out the broken tube(s).

You should be able to find a universal Choke Stove Kit,(Dorman 03840) in the Help! section of most auto parts stores. This simple, cheap kit (about $20) is designed to bypass the choke stove chamber on the exhaust manifold and replace the stock choke tubes completely. The kit comes with a length of coiled up aluminum tubing that you can easily bend by hand, the tubing insulation, the hardware to mount the tube to the choke cap, and a little "dome" with a hole in one end for the tubing to push into. This dome clamps to the exhaust manifold or header pipe to trap the hot air when the engine is running and routes the hot air up to the choke cap:



II. "Electric assist" choke cap
The "electric assist" portion of the stock choke system does not work on its own like an aftermarket electric choke. In fact, it doesn't have to work at all in order for the hot air choke to be effective. It is only there to "assist" the hot air choke in temperatures above 60 degrees, where it helps the choke come off sooner for cleaner emissions. It doesn't work at all when the weather is colder than 60 degrees. It connects from the spade on the choke cap by a wire that connects to the back of the alternator. This part of the choke is secondary, meaning the choke will work fine without it, but the choke will not work without the thermostatic "hot air" choke system.



The stock thermostatic "hot air" chokes with electric assist works MUCH BETTER than the fully electric chokes found on all aftermarket carburetors in that the choke opening corresponds with the engine temperature. As a result, the engine gets the right amount of choke it needs, and because it uses hot air generated from the engine, it doesn't choke the engine when it isn't needed.

Capiche?

 

I tried to "rep" you, LARIAT 85, but was reminded to "spread" the love!

 

I've been chasing a problem with a lack of power above 35 MPH. After replacing the O2, Temp and Throttle Position sensors I found the carb assembly was loose and decided to remove and rebuild it. That's when I found the broken tube. The orange hose has not been connected to anything for at least the last 10 years. The engine has always started fine but not with a high idle when cold and would sometimes need a couple of pumps of the gas pedal to keep idling. Recently at the gas station the choke plate stuck all the way closed and the engine would not restart. Fortunately the orange hose was available to stick in the intake and hold the choke plate open. After starting the choke stayed open without the assist of the orange hose. Ran fine after that aside from the original power issue. We'll see what happens when I get the tubes replaced and the carb back on. Thanks for the information.

 

Getting the hot air hooked back up to the choke greatly improved the engine's performance during warm up. The choke stove kit worked for replacing the fresh air tube from the carb intake to the bottom of the exhaust manifold but I had to use a 1/4 inch brake line with the flared end and male connecting nut to fabricate a hot air choke tube to go from the top of the exhaust manifold to the choke housing. Thanks to the education I received here on how the system works helped in making a fairly simple repair. Thanks again.