'75 1.8L Idling at 1,600 RPM -, Vacuum advance on distributor connected and... Options

[Rick986]

Had the car in for a post PI today and tech noted that the "vacuum advance" on distributor was not connected when the (previously bad) charcoal canister was removed. He teed into another vacuum line and connected the vacuum port. He noted that this will increase RPM's but will also help with acceleration.

I did notice a slight increase in acceleration but more so, the car is now idling at 1,600 RPM when warm. Seems excessive. Plus, I think that I noticed that the exhaust no longer "pops" when decelerating (which was kinda cool...yet slightly obnoxious).

Thoughts? Thanks for educating this Newbie...

[wonkipop]

i found this.
got curious about advance hooked up and retard left open on some L jets.
i shouldn't as sometimes its better not to think about EPA bone tipped spears and flint axes and just be dumbo. (IMG:style_emoticons/default/drunk.gif)
i annotated it for translation.




since i'm locked down in the worlds most locked down city its giving me too much time to think and not enough time to (IMG:style_emoticons/default/driving.gif)

if i understand the diagram right whats going on is if you snap the throttle shut on a 1.8 L jet with two vacuum lines from the distributor type of set up then the engine suction alone on the retard line is going to pull the retard back further than the at rest position at idle (it goes past where the springs would reach equilibrium). then as the vacuum weakens (revs come down) the springs take over again and advance the timing back up to idle position. the normal vacuum advance is completely closed by the snapped shut throttle. (an emissions thing on deacceleration if you close the throttle completely?)

this seems to correspond with how my car behaves particularly during the time the car is cold and warming up. if i give it a bit of a squirt before i drop the clutch, often just when i am moving it out to the door of the garage and close the throttle sharply it almost dies and then comes back up to idle. maybe they unhooked that vacuum line at some point in the production run to "cure" this behaviour so it just retarded down to idle setting where the springs equalise and no lower?

or conversely they never had to do this before the end of 1973 but had to introduce it at the start of 1974 to meet the emissions regs. when do they kick in? calendar year?