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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

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Old 01-31-2011, 12:39 AM
SatoriEnd SatoriEnd is offline
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1984 I-6 F-150 CARB Vacuum diagram

Figured I'd throw this up here for reference, and also because I need a bit of help with it myself.

Click the image to open in full size.

One of those lines used to be hooked up to my throttle feedback valve (looks like a little brass ufo on the rear of the carb on the right hand side facing the engine). However when I ordered a new carb (actually the correct carb according to the guys at Guaranteed Carb) this had a vacuum line attached to it from a point lower on the carb (same side) and the tube that did go to it is now left to just hang around.

The tube is currently connected on the vacuum tree (closest to the engine, closest to the front of the engine) but I have *no* idea where the other end hooks up.

Can anyone help me out? This and checking the charcoal canister are my last steps before I try to smog her again.
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Old 01-31-2011, 10:17 AM
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Franklin2 Franklin2 is offline
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I believe you are going to have to take a picture of the carb and the piece you are talking about. Do you still have the old carb so you can take a picture of that also?
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Old 01-31-2011, 01:37 PM
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I'll get pictures for you this evening Franklin, may be a little dark I'll do my best to get light on it. I do also still have the old carb (I'm planning to rebuild it at some point) so I'll include pics of that.
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Old 02-01-2011, 01:37 AM
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Ok here we go with the pics:

First up the loose tube end I have floating around:
Click the image to open in full size.

Next is where the other end connects to (roughly under my finger, it's a little tight in there for my hands sorry if they're in the way):
Click the image to open in full size.

And this is what it used to be hooked up to:
Click the image to open in full size.

Now as I pointed out earlier there's a new tube coming off of that brass bit there that wasn't on the old one. There's also a new nipple on the bottom right of the new carb that wasn't on the old one. I've been thinking about it and I've a sneaking suspicion that they get fed from the same place, but the output got moved at some point and Guaranteed Carb sold me a plate for the moved version.

This is the point (bottom right on the old carb) where there's an extra nipple on the new carb. That extra nipple is where the new tube is running from off the brass diaphragm ufo lookin' thingy.
Click the image to open in full size.

I have a few more photos of the new and old carbs side by side but this pretty much shows all the details.

Last edited by SatoriEnd; 02-01-2011 at 01:39 AM. Reason: Just noticed that I posted this exactly 12 hours from when I said I would.
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Old 02-01-2011, 06:25 AM
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The round gold thing is the choke pull-off. It gets manifold vacuum. Looks like the old hose hooks down on the manifold vacuum tree. From your description in the last photo, the new choke pull-off is already hooked to a fitting that is manifold vacuum coming out of the bottom of the carb.

So you can just cap off the line you are holding in the picture.

Click the image to open in full size.

See the round door in the top of the carb? That's the choke. See the large round casting at the top of the picture with 3 screws and a round black piece(can't see the black piece in the picture). That's the choke control or thermostatic housing. It has a round spring inside that works like a toaster, and opens the choke when it starts warming up.

When the engine is cold, you hit the gas pedal once, and the choke control shuts the little choke door on top of the carb completely shut. This is good for starting, but with the door completely shut, the engine would quickly stall out. So the round gold thing(choke pull-off) builds vacuum as soon as the engine starts, and it will crack open the choke a little bit to keep the engine running. That's what the vacuum line is for, to supply the diaphragm inside the gold thing with vacuum so it can pull the lever back.
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Old 02-01-2011, 12:56 PM
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Quote:
Originally Posted by Franklin2 View Post
The round gold thing is the choke pull-off. It gets manifold vacuum. Looks like the old hose hooks down on the manifold vacuum tree. From your description in the last photo, the new choke pull-off is already hooked to a fitting that is manifold vacuum coming out of the bottom of the carb.

So you can just cap off the line you are holding in the picture.

Click the image to open in full size.

See the round door in the top of the carb? That's the choke. See the large round casting at the top of the picture with 3 screws and a round black piece(can't see the black piece in the picture). That's the choke control or thermostatic housing. It has a round spring inside that works like a toaster, and opens the choke when it starts warming up.

When the engine is cold, you hit the gas pedal once, and the choke control shuts the little choke door on top of the carb completely shut. This is good for starting, but with the door completely shut, the engine would quickly stall out. So the round gold thing(choke pull-off) builds vacuum as soon as the engine starts, and it will crack open the choke a little bit to keep the engine running. That's what the vacuum line is for, to supply the diaphragm inside the gold thing with vacuum so it can pull the lever back.
Thanks Franklin! You confirmed my suspicions then. As for the choke pull-off thanks for clarifying the name, I know my mechanic would have gotten a laugh out of me calling it "the little brass UFO looking thing". I'll get that line plugged up down below (I like the new location more) and if the mechanic or state inspector asks what's up I'll explain that the port was moved.
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Old 02-01-2011, 12:56 PM
 
 
 
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