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TR6 Thermostatic vacuum switch

Ribbs

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More curious than anything; does the thermostatic vacuum switch allow vacuum to reach the retard unit at the distributor when the radiator water is cold or once the water is warm? The switch was already removed from my 1973 TR6 when I took ownership, with the vacuum tube going straight from the rear carb to the retard unit now.
 

poolboy

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There is a waxstat valve within the Thermostatic Vacuum Switch which prevented the vacuum from reaching the distributor's vacuum retard module when the coolant temperature reached the waxstat setting of over 200*F.
The effect was an increase in idle speed, fan speed and coolant circulation strictly due to the advance in ignition timing.
 
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Ribbs

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Thank you poolboy. I wonder then, without the thermostatic vacuum switch present if I wouldn't be better off just disabling the vacuum retard unit altogether. I believe that where the vacuum port is located the retarding action goes away as soon as the throttle comes off idle anyway. In that case would I leave timing at 4° BTDC at idle?

I do plan to send my distributor into BVU this winter for an overhaul including recurving mechanical advance and the addition of their advance module.
 

poolboy

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Retarding the ignition at idle is (was) an attempt to reduce emissions when the engine is idling...you can read a little on it here for the theory and nature of the emissions it's attempting to control.
http://www.georgiajag.com/Documents/Vacuum Advance versus Vacuum Retard.htm
If you disable it as many of us do, the ignition timing will advance as much as 14* to 16* depending upon the module, which will put the spark somewhere within the BTDC marks on your damper...10 to 12* BTDC at idle with a disabled retard perhaps.
Rob @ BVU will give you his recommendation for setting the timing with reference to the damper marks once he installs the Vacuum advance.
 
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