Wondering if someone can shed some insight on the thermo vacuum switch, I am trying to determine if mine is faulty. I installed electronic ignition (new distributor and coil) and I was setting initial timing (with vacuum line disconnected from the distributor vacuum advance of course). Got my timing set, but when I connected the vacuum line, I am not getting any vacuum advance? I only have three lines for the thermo switch, one to the back of the carb, one to the front of the carb, and one to the distributor vacuum advance. Im not getting any vacuum advance when the engine is cold or when the engine is up to temp. I have to connect to vacuum advance canister directly to the back of the carb to get any advance. Any insight would be helpful. This is on a stock YS 400 with a quadrajet carb.
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TxGTO69
Two sources of vacuum, ported and manifold. The engine under the 69 emissions system is tuned to operate on ported vacuum. When an overheat condition exists (230* and above) the thermo valve switches to manifold vacuum which advances the timing, increasing engine and fan speed when at idle.
The Ported vacuum source on an original 69 carb is on the middle right front of the carb, that line then connects to the middle left nipple of the thermo switch.
The Manifold vacuum source comes from the rear carb baseplate fitting that provides vacuum to the power brakes and auto trans modulator; that line connects to the lower left nipple of the switch.
The lower right nipple of the switch provides the sourced vacuum to the distributor advance.
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The Ported vacuum source on an original 69 carb is on the middle right front of the carb, that line then connects to the middle left nipple of the thermo switch.
The Manifold vacuum source comes from the rear carb baseplate fitting that provides vacuum to the power brakes and auto trans modulator; that line connects to the lower left nipple of the switch.
The lower right nipple of the switch provides the sourced vacuum to the distributor advance.
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