Vacuum lines on rochester carb

[81vettelover]

Hi all, Just installed non computer rochester q jet carb and distributor. Can someone tell me where is the proper place for the pcv line, the distributor line and the transmission line on the carb? Thanks Randy

 

[tomtom72]

Hi Randy, I do not know about the Vacume Modulator for sure, but the Vac Adv and the PCV need vacume from a constant source which means a source taken from the base plate (throttle plate) of the carb, or the intake manifold itself. I would think that the Tranny modulator needs vac from a constant source also as it interacts with the valve body to control shifting based on engine load conditions. Sorry I can't be more definitive about the trany line, but I'm sure about the PCV and Vac Advance. I know the higher up on the carb you go from the base plate, the vac siginal becomes subject to being periodic as those sections of the carb get called into use. Example: If you took vac off a port in the run circuit, it would not have a vac siginal at idle. Usually at the back of the base plate there is a big vac port for pure vacume siginal source. If your intake has a pipe plug in one of the runners you can use that as a source also. Sorry that's all I can add, I'm sure someone with more Knowledge will see this question and give you a better answer. tt72

 

[LilGTO71]

Randy, did you ever get the info you needed on hookup? Just wondering as I'm fixin to do the same thing. Thanks. John

 

[81vettelover]

81 vette non computer

Randy, did you ever get the info you needed on hookup? Just wondering as I'm fixin to do the same thing. Thanks. John

No I did not get the info yet. On a rochester carb there is one small vacuum line on back lower plate. one small on front left base (looking at carb) one small on right just up from base, one large under filter and one large above filter. I need to know where to hook distributor, tranny and pcv at. Thanks Randy

 

[RodsnRides]

On the early 70's Q-Jets I have worked on there is usually a large port at the back of the carb (down low, near throttle blades) that takes an NPT fitting with female flare for a pipe for your power brakes. The transmission vacuum line usually is a tap right into the intake at the top rear center-behind the carb. On the choke (vs. throttle) side of the carb there is usually a 1 1/2" long or so pipe for direct vacuum. This was typically the door on the air cleaner and is usually capped off. Moving to the front, the PCV (3/8") line is just below the fuel inlet-between the mixture screws. That should leave one fitting left, up to the right of center front that is typically the vacuum advance to the distributor. Sometimes its a small fitting like the one on the choke side, sometimes it's about 1/4" in size. That should get the car running, then use a vacuum gauge to confirm that it is getting vaccum after 1500 RPM or so-you really don't want vacuum advance at idle. I don't run it, anyways. Hope this helps.

Rick

 

[81vettelover]

81 vette

On the early 70's Q-Jets I have worked on there is usually a large port at the back of the carb (down low, near throttle blades) that takes an NPT fitting with female flare for a pipe for your power brakes. The transmission vacuum line usually is a tap right into the intake at the top rear center-behind the carb. On the choke (vs. throttle) side of the carb there is usually a 1 1/2" long or so pipe for direct vacuum. This was typically the door on the air cleaner and is usually capped off. Moving to the front, the PCV (3/8") line is just below the fuel inlet-between the mixture screws. That should leave one fitting left, up to the right of center front that is typically the vacuum advance to the distributor. Sometimes its a small fitting like the one on the choke side, sometimes it's about 1/4" in size. That should get the car running, then use a vacuum gauge to confirm that it is getting vaccum after 1500 RPM or so-you really don't want vacuum advance at idle. I don't run it, anyways. Hope this helps.

Rick

Rick thanks alot.... Your a hero. Now all we need is some sun in Western PA and ready to cruse. Thanks again. Randy

 

[RodsnRides]

Q-Jet vacuum ports

Rick thanks alot.... Your a hero. Now all we need is some sun in Western PA and ready to cruse. Thanks again. Randy

My pleasure. I got to thinking after I sent that note, the Q-Jets after '72 started adding fittings for various devices like EGR, TVS, etc. If I need to use a later carb-I block them all off other than the ones I already mentioned. If you have a big 3/8" barb at the top near the air cleaner "ring" that is the bowl vent that went to the charcoal canister. I cap it off, too. And any at the back of the carb, too. I only use the ones I mentioned in the earlier note. Works for me. All my stuff is '70-'72 vintage, except my lady's '67 GTO. Have an originnal Ram Air Q-Jet for it, bit missing all of the choke side. Any lead on '67 Pontiac Q-Jet parts in PA? Yeah, I know, this is a Vette site, but I had to ask. Thanks,

Rick

 

[LilGTO71]

Randy, try Year One, Ames, or Original Parts Group. I just rebuilt by 71 Q Jet and didn't get everything in the rebuild kit I needed. Looking at my receipt it was Original Parts Group (OPG).

John