Carburator vacuum line routing

[The_Handier_Man1]

From: bobdonaghy01  (Original Message)
Sent: 4/6/2004 5:12 PM

I just had my rochester quadrajet carb rebuilt. I thought I could remember the vacuum line routing. Guess what. I think the ones on the front of the engine are connected up ok but I'm not sure about the ones in the back. There is something located on the intake manifold close to the carb on the passanger side. It has 2 steel lines coming out of it. One of the lines heads towards the back of the carb, but I dont know where it connects. There are 2 manifold ports on the back. One for the brake system and the other ?? There is 1 carb vac. fitting high on the carb, that I think hooks to the distributor vac. advance.
Appreciate any help

Bob



From: denison
Sent: 4/6/2004 7:24 PM

Other things that need vacuum connections include the pcv valve, a cruise control diapragm, the vacuum operated heater contols like some vehicles started having in the late 70s. Does you rig have an EGR valve? Does it have a vacuum gauge? Even if your rig didn't have a cruise control, they might have had a nib on the manifold for the option. My Holley carb has two vacuum ports for use with the vacuum advance on different types of distributors. Mine seems to run just the same no matter which one I am connected to, and I just cap off the other port. Good Luck.



From: Sea Hag
Sent: 4/6/2004 9:49 PM

What year and type is your chassis and what engine do you have . - I have info for mid to late 70's dodge vacume /emisshions system that might help -- Sea Hag 



From: bobdonaghy01
Sent: 4/9/2004 2:38 PM

well I finally got it straightened out. solved the puzzle of the vac lines. discovered vac advance can on distributor was froze up. evidently hadnt worked in quite a while. bought new cap, rotor and vac advance. and installed. I should have thought something was wrong with timing cuz under moderate to hard acceleration, the engine would ping. got everything together and took out on the highway. engine still had a ping so I loosened the distributor clamp bolt and twisted the dist a little clockwise. smoothed out nicely. no more ping. also got the 4 barrels to open up nicely at wide open throttle. what a kick in the pants. I now have much better torque and throttle response. the mh scoots quickly up to highway speeds. now I'll have to see what effect the changes have on gas mileage. 



From: Jhoffa_
Sent: 4/10/2004 6:40 PM

Rule of thumb for vacuum lines:

There's two types of engine vacuum: Ported and Manifold.

Manifold Vacuum is high at an idle and goes low when you open the throttle. Ported Vacuum is the reverse.

Manifold vacuum ports will be found BELOW the carburator's throttle blades. Ported vaccum ports will be found above.

Aside from that & provided they're the correct size.. Hook them up anywhere you wish provided your accessory get's the correct vacuum type.