Mystery Carb Lines
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Mystery Carb Lines
Hi all, My '86 van 4.9 carb has two dangling lines, and I'm not sure what either does or where they should connect.
The first comes off the electric choke, and I suspect it connects into the exhaust manifold down by the heat riser valve. But I'm not sure if it transfers heat or pressure. I'm guessing heat, and that this tells the choke to turn off - and that's why I have hard smokey rich starts ten minutes after shut off in the summer. If it's heat, can I just make a new tube out of copper and slip the remaining insulation over it?
The second tube led to the top of the carb opening, and a previous mechanic had a rubber hose attatched to it and I don't know what. I've no idea what it does or where it should go.
I've got driveability problems with the van, and I'm hoping these fixes will help. The engine can bog under load, especially when it's colder. The TFI distributer has all new cap, rotor, wires, plugs, so I think that's somewhat sorted.
Thanks for any tips!
Steve
The first comes off the electric choke, and I suspect it connects into the exhaust manifold down by the heat riser valve. But I'm not sure if it transfers heat or pressure. I'm guessing heat, and that this tells the choke to turn off - and that's why I have hard smokey rich starts ten minutes after shut off in the summer. If it's heat, can I just make a new tube out of copper and slip the remaining insulation over it?
The second tube led to the top of the carb opening, and a previous mechanic had a rubber hose attatched to it and I don't know what. I've no idea what it does or where it should go.
I've got driveability problems with the van, and I'm hoping these fixes will help. The engine can bog under load, especially when it's colder. The TFI distributer has all new cap, rotor, wires, plugs, so I think that's somewhat sorted.
Thanks for any tips!
Steve
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Joined: Apr 2005
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From: South Bend, IN
The choke thermostat input comes from the heat chamber by the #5 cylinder output on top of the exhaust manifold. The input to that heat chamber is on the bottom of it through a 1/4" hole on the side opposite the engine, a metal tube connects to there and goes up and connects to that 1/4" air horn connection you described with a rubber hose. If you also insulate the inlet tube from the air horn the choke will pull off faster. Also make sure the choke thermostat cap assembly has the correct gasket between it and the carburetor, and be sure to tighten down the three holddown screws tightly after making adjustments to avoid leaks and insure that the system pulls as much heated air as possible through this plumbing.
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Hi Brian,
Thanks for the reply. I've looked at the engine, saw all you mentioned that I'd never noticed, thought about it and have these questions.
If the "circuit" for this heat tube system begins at the top of the carb opening, wouldn't this tend to draw air and heat into the motor? Why would we want this?
How does the heat travel to the carb? Does it meander up there, or is there some kind of draw?
The tube leading to the choke is broken while stuck into the manifold, with an inch protruding. Is this just pressed in? Pull it out and press in another?
Where would I find a tube for this? Someone on this site wrote "look in the Help section", but I have not found that.
Thanks for your knowledge - I'm delighted to find a site like this. Good thing my van motor went into pickups too, or I'd be out of luck.
Thanks for the reply. I've looked at the engine, saw all you mentioned that I'd never noticed, thought about it and have these questions.
If the "circuit" for this heat tube system begins at the top of the carb opening, wouldn't this tend to draw air and heat into the motor? Why would we want this?
How does the heat travel to the carb? Does it meander up there, or is there some kind of draw?
The tube leading to the choke is broken while stuck into the manifold, with an inch protruding. Is this just pressed in? Pull it out and press in another?
Where would I find a tube for this? Someone on this site wrote "look in the Help section", but I have not found that.
Thanks for your knowledge - I'm delighted to find a site like this. Good thing my van motor went into pickups too, or I'd be out of luck.
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From: Fraziers Bottom, WV
The lower manifold pressure at the bottom of the carb will draw the air from the top of the carb through the chamber and to the choke. This is heated air and helps the choke open and close as needed for the temp. outside. you can get the lines from any autoparts in the "HELP" parts section!
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Joined: Apr 2005
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From: South Bend, IN
I have heard that it is getting hard to find the heat riser tubes in the "HELP" parts section of the auto parts stores. I used 1/4" copper tubing for my heat chamber inlet line because that's what I had laying around. A steel brake line would probably be the best, but you will probably need a tubing bender to bend it without kinking it. You can get the high temperature insulating tubing from a number of on-line auto parts stores, just google 'choke tubing' and see what you get. As long as it's long enough it doesn't matter what vehicle it's designed to fit.
The system will work without the inlet line from the carburetor air horn, but it will draw in filtered air if you hook it up, which is why it is there in the first place.
The system will work without the inlet line from the carburetor air horn, but it will draw in filtered air if you hook it up, which is why it is there in the first place.
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Hi Brian,
Yes, a quick tour of my local parts stores got some puzzled looks and nothing more.
I'm still mystified by what you all mean by the "Help" section. I've used the "Search" features... is this what you mean? No luck there, but I'll try your keywords.
I can't think of any superiority of steel in this application. Copper would transfer heat even faster I would think. I can reuse the old fabric insulator. I'll have to get a flare on the end though.
Steve
Yes, a quick tour of my local parts stores got some puzzled looks and nothing more.
I'm still mystified by what you all mean by the "Help" section. I've used the "Search" features... is this what you mean? No luck there, but I'll try your keywords.
I can't think of any superiority of steel in this application. Copper would transfer heat even faster I would think. I can reuse the old fabric insulator. I'll have to get a flare on the end though.
Steve
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Oh, one more thing. Were these metal tubes just a regular tube and they pressed into the hole on the manifold? No special fitting? Thanks.
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From: South Bend, IN
The "HELP!" section is a line of universal fit aftermarket parts carried by many auto parts stores. They are typically used where OEM parts are no longer made. They are packaged in bright red packaging with HELP! in big letters.
The metal tubes are just pressed into the holes in the manifold. You will likely have to clean out the holes of rust and the remains of the old tube with a 1/4" drill bit. BTW, the fitting on the choke housing on my truck is a compression fitting, not a flare. If yours is like that you will just need to pick up a 1/4" nut and ferrule to make the connection.
The metal tubes are just pressed into the holes in the manifold. You will likely have to clean out the holes of rust and the remains of the old tube with a 1/4" drill bit. BTW, the fitting on the choke housing on my truck is a compression fitting, not a flare. If yours is like that you will just need to pick up a 1/4" nut and ferrule to make the connection.
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Hmmm. I know I will sound ignorant, but I was thinking I needed a flare because when I removed the broken pipe from the choke connection, it had a flare on it. Did the two nut and "ferrule" (new word for me) create that?
BTW Brian, (per your user profile) I'm curious how you got intermittent wipers for your truck using OEM parts. I've always wanted that for my van!
BTW Brian, (per your user profile) I'm curious how you got intermittent wipers for your truck using OEM parts. I've always wanted that for my van!
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From: South Bend, IN
Maybe the fitting on your carb is different from mine. Use whatever you have to to match up to what's there.
The intermittent windshield wipers is a simple mod. Just get a wiper switch and control box from a junkyard and they plug together in place of your current switch. Mine cost me $50 I think. If you do a search of this site you will find it discussed many times.
The intermittent windshield wipers is a simple mod. Just get a wiper switch and control box from a junkyard and they plug together in place of your current switch. Mine cost me $50 I think. If you do a search of this site you will find it discussed many times.