'77 fj40- yet another stock dizzy (theory)question

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May 25, 2016
Hey there dizzy experts- my recently acquired (mfr'd 5/77) is all stock and original, with a single diaphragm one hose vacuum line dizzy, semi-electronic w/ igniter. I don't know if it's a retard or advance unit. when I manually(mouth!) apply a vacuum, it does rotate the points plate as hoped. My thoughts are, (please correct me if wrong) under light throttle= high vacuum= plate turns= retards timing. Heavy throttle= low vacuum= no retard/more power. But... if it's an advance mech., then it doesn't make sense!?! Please enlighten me? Thanks to all!
It's advancing for the EGR system.
EGR requires a lot of advance when it kicks in.
Output shaft- Ok? I don't understand the theory behind the EGR's role in that scheme. Would you please explain more for a newbe? Thanks!
Here's the Wikipedia explanation:

Exhaust gas recirculation - Wikipedia, the free encyclopedia

Since the EGR diluted mixture contains less oxygen (recirculated exhaust), it burns slower. A slower burning mixture requires an earlier spark in order to burn efficiently.

On our carbed engines, the EGR valve opens when the throttle plate passes the advancer port in the carb throat. At that time, both the EGR valve and vacuum advancer on the distributor actuate in tandem...Or at least they were supposed to when the engine was new.

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