This is my first post, and I have been searching around this site and learned quite a bit... like my carb is a 2150. A lot of the stuff from my '76 has been removed and/or butchered and it really hasn't been running in 15 years. I rebuilt the carb and reset the choke (thanks to a great tutorial from this site), but still have a few questions. The heat tube that connects to the choke is missing, where does the other end connect to? The exhaust manifold (mine is missing the reat riser manifold shroud), or the intake manifold? Also, after the truck starts, how long typically does it run until the choke opens? When you bump the pedal after its running to lower the idle, does that just kick the idle cam to a lower step or is it also supposed to retract the choke plate too? One more question... would driving the truck for a few miles with the choke fully closed (missing heat tube, remember?) cause the carb to be flooded enough so it wouldnt start up again?

 

Welcome to FTE!

1. The choke heat tube connects to the intake manifold. The heat riser on the exhaust is for a separate mechanism. If you don't fix this, your choke will never open.

2. The amount of time it takes the choke to open depends on climate, but typically it should be open after 3 or 4 minutes. If it's freezing cold outside, it will take longer of course. In general it takes about as long as your engine takes to reach operating temp.

3. When you bump the throttle to lower the idle, all that happens is the fast idle cam drops to the next available step. It won't affect the choke. The only thing that can open the choke is the choke spring itself.

4. No, driving for a few miles with the choke closed will not prevent it from starting again. Remember, the choke is on for the first few miles of driving anyway. However, once the engine is up to temp, if the choke stays on, the motor will have trouble staying running. You'll be able to drive around somewhat, but it won't idle.

 

Great info, thank you very much. Where on the intake does it connect? Its just a conduit for warm air isn't it? Is it a metal tube with flared ends similar to a fuel line? Thanks again for the info, it was your tutorial that helped with understanding the high idle linkage.

 

Yes, it provides warm air to the choke. It usually connects to a flange on the intake on the passenger side. It connects to the choke with a flared end and a flare fitting. I can't recall how it connects to the intake; it has been a while since I looked at it. I don't recall it being a flare fitting on that side. I'd have to go out to the garage later. It's a metal line like you could use for fuel line or transmission line, etc. Glad the write-up helped.

 

i'll find the spot, thanks again

 

The only place I can find that the tube can attach to is a threaded hole (about 3/8) on the very back of the intake, right next to the last intake mounting bolt,kind of under the egr valve. But the hole is full of all sorts of crap. Does this sound right? Also my choke has a wiring connected to it, is this normal for a mechanical choke or did someone swap it out for an electric one in the past? It does have the thermo-spring inside, and adjusts like a mechanical one does. Thanks -Jason

 

You know, chokes are just plain ol' bad for an engine. :/
...of course running way too lean is too tho! :/
The trick is to not use anymore choke than you have to. :)
Adjust it to meet yours and the engine's needs and not much more.

YMMV

Alvin in AZ

 

The wiring is for electric assist. It sources from the stator of the alternator, and is supposed to be there. I'll have to go out and check about the hole on the manifold. What motor is this?

 

It is a 302 from a '76 F-100. I'm not really sure if the hole goes all of the way through, just when I probe it with a screwdriver, it has debris inside of it

 

I've done some searching on this site and I still cant really find where it attaches. I found the rubber "fresh air" tube coming from the top/rear of the airhorn, but there isnt anything for it to attach to. I am apparently missing some air chamber thing. The only likely place I can see is around the carb base plate somewhere near the Egr. Does anyone have a picture, or a good description where the choke heat tube attaches? Thanks -Jason

 

Sorry this took so long. Here's a shot. It's between the passenger side of the carburetor and the passenger side valve cover on the top of the intake manifold. One tube is for heat, the other is for vacuum to cycle the warm air.

 

Thank You, I know it's a pain to take everything apart and take a picture. I found the two hold down bolts in the picture, but there is definitely no little housing thing for the tubes. The hood weather strip is long since gone, so everything is pretty much rusted away on top of the engine. Is it just a little enclosed space that gets heated up by sitting on the intake? I could probably just fabricate something. Is the tube coming from the air horn rubber? And where does the air cycle to once it reaches the choke? Sorry, for the multi-questions...

 

I am trying to pull this from memory, so bear with me.

The metal line that connects to the air horn on the carburetor using a short length of rubber hose should be manifold vacuum. The vacuum signal goes from there to the inside of the choke housing. The choke housing mounts to the passenger side of the carburetor through three stand-offs. One of the standoffs is wide because there is a small passageway for the vacuum to travel. That's why when you rebuild a carburetor, there is a small gasket for this spot. The vacuum is introduced to the inside of the choke housing through a small hole. I believe if you remove the choke cap with the engine running, it exposes the vacuum source and the motor runs rough and\or stalls. This vacuum signal is what gets the air moving.

The other line is for hot air, I believe it comes from an exhaust crossover, but I haven't looked myself. Without the vacuum signal, the hot air wouldn't be drawn into the choke. The vacuum line creates negative pressure in the choke housing. Because the hot air line is also connected to the choke housing, the vacuum signal pulls in hot air into the housing, which heats up the spring.

I'm not sure how things look underneath the plate on the manifold that holds down the two lines. One obviously goes to an exhaust crossover and one goes to manifold vacuum, but I don't know if it's a flare fitting inside, or what. If all this is too much trouble, my advice would be to plug both sources, and install an electric choke. You should run the choke power from the stator terminal of the alternator, if you go this route. Some people prefer manual chokes, and you could of course go this route as well.

 

Okay, now everything is falling into place. Considering I am missing this entire circuit, some other type of choke sounds better. I bet an electric choke wont be able to use the electrical connection that's already there, will it? Thank you again for your help.

 

What connection is already there? Does the choke that's already on there now have an electrical connection? These are called hot-air with electric assist chokes.