vacuum line help

[derekb]

Okay, I would flunk "are you smarter than a fith grader" when it comes to my 72 project...but I am learning every step of the way. PO removed all vacuum lines and I am trying to reconnect. California truck and evap can and vacuum advance are going to nowhere. So where should they go. I'm thinking vacuum advance would go to the carb but want to make sure right place on the carb. I'm sure I'll be asking more but for now this would help. Thanks!

[Sinister]

Vacuum advance to manifold vacuum on the carb. Sorry, can't help with the emissions stuff.

[Leviticus]

Actually you want your vacuum advance hooked to your "Timed Vacuum" port, and all your other stuff like brake booster, tranny modulator etc hooked to manifold vacuum.

[Sinister]

Timed or Ported vacuum was a emissions crutch from the 70's, the truck will run much better with manifold vacuum to the vacuum advance.

[Leviticus]

Originally Posted by Sinister

Timed or Ported vacuum was a emissions crutch from the 70's, the truck will run much better with manifold vacuum to the vacuum advance.

Never knew that, I'll have to give that a try.

[Jacfourteen]

Originally Posted by Leviticus

Never knew that, I'll have to give that a try.

Yep they did that so that idle emissions are lower, but it makes the engine run hotter at idle and causes other issues as well. Holley and other carb manufactures still recommend using the timed port, but most carb tuners say use full vacuum for distributor. I changed mine over to the full vacuum and it Idles much smoother now.

[cdowns]

factory assembly manuals have excellent diagrams of correct vaccume line routings// they still use textbooks in the fith grade its called book learnin a concept younger adults dont seem to grasp anymore

[dwcsr]

Originally Posted by Sinister

Timed or Ported vacuum was a emissions crutch from the 70's, the truck will run much better with manifold vacuum to the vacuum advance.

I have to disagree with this. If you run manifold vac to the dist you then retard timing on acceleration or WOTonce the vacuum is gone or lowered. Timing advance is better utilized at higher engine speed rather than lower. Running manifold vac will also counteract he centrifigal weights leaving you with an almost static timing not much above the intial timing at high speed and full advance timing when you are off throttle or on deceleration when its useless to do that.

The emmision setup on these old trucks was to retard timing with the spark control unit until it hits a certain temp and speed in drive then it allowed for full advance as dictated by the butterfly opening.

[John H.]

I can give you a start. On a 72, there was a solenoid that mounted on the pass rear side of the intake ( would not let advance to the dist until the engine was warm or the car was in 3rd gear, Should be a sensor on the passenger side head and wires going from the solenoid and the sensor to the transmission). I believe, the dist vac advance went to this solenoid and the other port on the solenoid went to the front of the drivers side of the quadrajet vac port. I think this might have been teed and that hose went to the small port on the charcoal canister. The PCV hose went over to the large port on the front/bottom of the quadrajet and that hose T'd 3/8 dia went to the charcoal cannister along with the smaller vaccuum tub teed from the front of the carb. The other port on the charcoal cannister was the vent line back to the tank. This hard line is on the frame. The long/thin tube on the passenger side of the quadrajet near the choke pulloff linkage was for the vaccuum hose on the air cleaner to operate the flap on the front of the snorkle. If you can the smog pump, there was a vaccuum line there too, but I am not sure how those T'd or were routed.

[OhioDan]

Does this help any?