Vacuum leak on 300 CI 6 CYC
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Joined: Feb 2000
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From: Ft Eustis VA USA
Vacuum leak on 300 CI 6 CYC
Hello. I have a 1985 F-150 with the 300 CI ^. There is a metal vacuum line that hooks up to the choke. The line rusted through at the bottom and is leaking bad. Does anyone know where the bottom of the line goes to? I've looked and can't seem to find it anywhere. Greg.
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Joined: Jan 2000
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I don't know if this helps in your case, but I can describe a common V8 non-electric choke heater setup.
Clean air from air cleaner or top of carb is piped to a metal plate bolted onto the intake manifold. This metal plate has two tubes on it. It is an exhaust-gas heat to air heat exchanger. Even though it is in the intake manifold, it is heated by exhaust via an exhaust crossover passage in the intake manifold. So the air goes into this "exchanger" (can just be a coil of tubing), picks up the temperature of that area, then goes up to the choke housing, warming the bi-metallic coil inside. Then into the carb through a small vacuum port.
As the block and intake warm up, the exhaust temp in the crossover gets hotter and hotter, as the metal around it is not cooling the exhaust down as much as when the engine was first started. So the choke bimetallic coil roughly tracks the engine temp, till the choke is wide open.
If you have a system like this, besides tubing rust-through, is rust-through of that heat exchanger, which often blows carbon up into the choke housing, and it stops working till the orifice in the carb is cleaned (if plugged), and tubing and exchanger replaced.
Don't know if that helped.
[This message has been edited by Granpa (edited 09-27-2000).]
Clean air from air cleaner or top of carb is piped to a metal plate bolted onto the intake manifold. This metal plate has two tubes on it. It is an exhaust-gas heat to air heat exchanger. Even though it is in the intake manifold, it is heated by exhaust via an exhaust crossover passage in the intake manifold. So the air goes into this "exchanger" (can just be a coil of tubing), picks up the temperature of that area, then goes up to the choke housing, warming the bi-metallic coil inside. Then into the carb through a small vacuum port.
As the block and intake warm up, the exhaust temp in the crossover gets hotter and hotter, as the metal around it is not cooling the exhaust down as much as when the engine was first started. So the choke bimetallic coil roughly tracks the engine temp, till the choke is wide open.
If you have a system like this, besides tubing rust-through, is rust-through of that heat exchanger, which often blows carbon up into the choke housing, and it stops working till the orifice in the carb is cleaned (if plugged), and tubing and exchanger replaced.
Don't know if that helped.
[This message has been edited by Granpa (edited 09-27-2000).]
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Joined: Aug 2000
Posts: 1,759
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From: Friendswood Texas
i think that line rusted on my 84 and i just pluged it up. I hope your experience is better than mine. HAD AN 84 F150 WITH A THE SAME ENGINE. I GOT IT NEW AND SOLD IT IN 1992. IT LIVED UP TO ITS REPUTATION...THE MOTOR NEVERHAD A PROBLEM HOWEVER i did replace:transmission,rebuilt rear end, rebuilt front end, had to do brake job on right front disc every 10,000, rebuild carborator, altenator, fuel pump, new exhaust system, a/c compressor and evaporator, all while getting a steady 11 mpg. thank god they dont buildem like they used to! the guy who bought it from me has drove it from houston to alaska twice...same engine.