Vacuum Related Question
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Freshman User
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From: Illinois
Vacuum Related Question
I was wondering if the vacuum ports off the thermostat housing need to be plugged up. There are no lines leading to them anymore and i was wondering if i need to cap them. Its a 79 f150 with a 351M
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From: chicago burbs
if there are no lines going to it then it's just an abandoned vacuum switch. normally, one nipple is connected to a vac source and the switch operates by temperature change to control where the vacuum is applied. you could get a pipe plug of the correct thread size and remove it completely if you want to
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Hmmmm, that little switch may be the one that is supposed to switch vacuum sources for the advance.
When the engine is cold the advance is supposed to be hooked to full manifold vacuum. When the engine warms up the vacuum is switched to ported vacuum. Some switches also switch back to manifold vacuum if the engine overheats.
Manifold vacuum == strong vac at idle.
Ported vacuum == weak or no vacuum at idle.
When the engine is cold the advance is supposed to be hooked to full manifold vacuum. When the engine warms up the vacuum is switched to ported vacuum. Some switches also switch back to manifold vacuum if the engine overheats.
Manifold vacuum == strong vac at idle.
Ported vacuum == weak or no vacuum at idle.
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Freshman User
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From: Illinois
Well the old truck has been running rough and it pings under acceleration. lol, Is there some sort of special connector that plugs into the switch and then a line that goes to the vacuum advance???
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Nope just three vacuum hoses. The center port goes to the advance. I don't remember which of the other ports is for which type of vacuum. I just put a line on the center port and blow thru it when the engine is cold to identify the manifold vac connection.
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From: Illinois
This may be a dumb question, but where does the manifold connection go to, i assume a port on the manifold somewhere???, So the middle port on leads to the vacuum advance, then one of the others goes to the manifold vacuum port, then what about the last one??? sorry but im not a expert on vacuum systems.
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From: chicago burbs
you didn't mention any driveability problems before i suggested to remove it. if the center one is to the distributor, then blow through it while the engine is cold and see where the air blows out. this connection would go to direct manifold vacuum. then, get the engine all good and warmed up, and blow though the center one again. the air should come out the other connection this time. if it does, then that connection is your "ported" or "timed spark" connection from your carb. what kind of carb do you have?
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