I'm replacing the old 2 bbl with a new 4bbl Q-jet rebuild from Summits, and there are at least 6 vacumm ports, and a couple other hook ups on it. Does anyone have a photo and or description of what goes where? This is my first 4 bbl Q-jet so I'm totally in the dark.Or possibly a book with photos that show the layout. BTW this carb has an electric choke. Looking through the archives someone made mention of a guy here in Mich that rebuilds q-jets anyone with a name a number? Thanks guys you've been great, Barry
These ports are easier than you think. The large vacuum port, as on the 2bbl, is used for the PCV system. The other ports, the manifold ports, are used for the air cleaner, choke pull off, and the vacuum advance. If the carb has a rear choke pull off, it should be used by the air cleaner temp sensor. It will be controlled by air cleaner temperature, and will widen the choke plate's position when the air cleaner is above 100 deg. Ported vacuum will be used for the bowl venting, through the vapor cannister, and EGR, if equipped. Questions? Ask either here or through the private messaging. Ray
Hi Ray, thanks for taking the time, as I know you are a Q-jet guru and know your stuff!! This motor has a manifold off some unknown year 350 Buick, and I am trying to elimenate as much smog crap as possible off it. There are plenty off fitting holes manufactured into the casting but no fittings, same with the carb, plenty of ports coming off it also. I have blocked off the EGR port and also the area where the old mechanical vaccuum goes as a new electrical vaccuum came with the carb. This motor is going into an old 51 Willys and I'd like to keep the engine compartment clean yet if needed I will hook up all the extra BS if functionally neccassary. As far as specfic questions -well here goes- for starters-On the manifold in front of the carb is a "tree" with three places for hoses, where do these go? Will pictures of the carb/manifold help? Any manuals available showning the routing of all these ports, dawg it sure is a puzzle :>( Thanks for helping, Barry in Mich.
The tree you refer to is the thermal vacuum control for the cannister purge system, preventing purging during cold operation. You are fortunate regarding the integration of these emissions controls. They will only adversely affect the engine if they are installed. If they are not, the engine's performance will improve. Since it is going in an older vehicle, emissions issuer are moot. Though I do not condone the disconnection of emissions controls, their removal may be essential to the performance of the '51. Please do not hesitate to ask questions if you have them.
Thanks Ray, and yep, no vaccuum cannister on this ride. I guess a simpliest question to ask would be , which vaccuum lines are essential to have hooked up in order to avoid mal-function or an ill running engine? Or possibly I can ask which lines can be avoided?<G> This is not a daily and will not see much winter use here in Mich. Thanks, Barry
Barry, Very simple really. On most stock motors, there are several vacuum lines coming off the carb. You can remove the thermovacuum switch and use the hole for a temperature gauge. There are 2 types of fittings coming off the carb. One is full manifold vacuum, and the other is timed, or ported vacuum. There is a full manifold vacuum nipple at the rear of the carb that feeds a vacuum cannister(for operating the heater control valve, and climate control doors). As Ray said there is a 3/8" fitting at the front for the PCV valve. The only other necessary vacuum conection is for the distributor vacuum advance cannister. You decide whether you want to run ported or full vacuum to the advance cannister. If you are using a thermally conmtrolled air cleaner, the sensor gets full vacuum. Other than that, there are vacuum nipples for the choke pull offs(some carbs have 1, others 2). Anything you don't use, block off.
You mean I can block off all those nipples on the Q-Jet and she'll run fine? The only hose that I need to connect, as far as I can see, is the line from the Vac. advance on the Dist.. I also will need to plug up several holes on the manifold , but hopefully that will do it . Thanks, Barry
Yes, the only line you must connect is the PCV in the front. Then run one line to the vacuum advance. There are usually 2 vacuum take offs on the intake manifold, one for the transmission vacuum modulator, and one for the power brake vacuum supply.
Rather than running the PCV line, can I run the old style valve covers with the oil breathers instead? Thanks again, Barry
You can run the old style road draft tube set up, but one of the reasons the PCV is there is to better vent the crankcase. The vacuum set up is more effient at this than using the pumping of the pistons to evacuate the crankcase, and the carb is metered for the vacuum leak encountered. If the hose is plugged, the crankcase venting will be only possible by the pumping of the pistons, and the carb will be rich. I strongly suggest the PCV, as GM designed it. Ray
OK Ray, thanks for the info. Now then,if I chose to run the PCV,it comes out of the back of the intake right? The new air filter doesn't have a port to connect it to, so do I plug it into the carb? If yes, that's great except I don't know which port,there are at least 3 big tubes in the front of the quadro and one real low fitting on the back of it. Any idea? That is one of the reasons for no wanting to plug it in, and go with the valve cover breather. Thanks for the time and help. Barry
Barry, There should be a single large 3/8" fitting on the front of the carb. Connect a 3/8" piece of fuel line to that fitting, and route it to the PCV valve in the rear of the intake manifold. Then stick a breather in the valvecover, and you are done, simple as that. If there are more big fittings in the front of the carb, only one will pull vacuum, thats the PCV valve. I've never seen a Q-jet with more than one large fitting, although some may have had one for a vapor cannister. The low fitting in the rear is for the vacuum supply to operate the heater doors and climate control, you can plug it if not needed.
Larry/ Ray- others, I did an in depth look at the tubes coming out of the carb. Here is what I got: Front: There are two 3/8" tubes coming out of the front of the carb. One is on the passenger side coming straight out of the base. The other is center upper and angling down on a 45 towards the manifold. Also three smaller tubes probably 1/4" One on passenger side -carb base plate coming stright out but pointing towards the alt. One above it at the top of the carb pointing the same way. One on the driver's side a little less than half way up and coming stright out. Rear : Top center of carb is a tube probably 3/16" coming straight out facing firewall. bottom center of base plate is a hole for fitting. bottom passenger side is a 1/4" fitting that is connected to one part of a "T" , one other part goes to the Vac can on the electric choke- no idea what goes to the "other" leg of the T . That's it -clear as mud? So now - Front here is my guess- 3/8" tube from passenger side front base goes to the PCV- block the other 3/8" -right? The 1/4" tube at the top of the passenger side goes to the Distributor -block the other two -right? Rear Block top center 3/16" tube Block bottom center base passage hole Don't have a clue what goes into the third leg of the "T" that connects to the electric choke . Help!! <G> Barry
OK, The 3/8" coming out of the base is your PCV connection. The angled 3/8" is for an emissions cannister, block it off. Use one of the 1/4" fittings for your vacuum advance. Ported vacuum should be on drivers side, full manifold on the passenger side, your choice. Block everything else.
This is to update those concerned with the myriad of hose connections on the front of this carb. This unit had several vacuum controlled emission controls connected to it, including the thermal air cleaner, the vapor cannister, and on some models, EGR. Yes, I have seen EGR on some '73's. Though this was rare, it happened. The thermal air cleaner was used to enhance cold performance during this operation, and its use will depend on the climactic conditions under which it is used. Tepms below 45 deg, and relative humidities above 50% will require the use of the thermal set-up. This is due to the relative air velocity through the primary barrels. The high velocities, and the fuel vaporization will lower air temps significantly, creating icing on the venturis. The use of the temperature controlled set up will also enhance cold operation, since warmer air requires less fuel. The loss in performance is minimal, and the increased driveability will benefit. The vapor cannister vents both the carb bowl and the fuel tank, and is how the systems were designed. Changes in fuel metering will result from these systems being bypassed. They are easy to connect and I woul;d be happy to help anyone with these problems. Ray
Thanks Ray, I got onr for ya I'll bet you haven't ran into before. Went to Murray's ( discount auto store here in Mich) a bought a new rubber grommet for the PCV and also a new PCV. The guy looked up the part numbers and danged if they didn't have them. So after the 20 mile round trip I come home put in the rubber , grease the hole and try to push the PCV in, man it's tight. OPPS! Pushed the grommet through the hole and I can't see it. S--t!!!!!!!! I can't see it and hope it didn't go down the intake hole. Pulled the carb back off hoping I can see it through the carb bore. Nope ..... Can't find my handy dandy mirror on a stick ..................to look for it I know the wife's finchs have a mirror and the stupid things ought to know by now what they look like , so I swipe it, break it to pieces and glue a small piece on a stick and go diving ..... Finally find it and use the tool that has a plunger on the end that when you press it the other end opens like those games at the carnival. Ten minutes of fishing and I get ahold of it and get it to the hole which is to small for it to come through now :>( Quickly I grab a small screw driver and am able to put the shaft through the hole and PRY it out.
Opps I'm still shaking..................... Any way, finally, it's out, I get the drill and enlarge the rubber hole, and in a minute I grease the hole , the PCV and put them back together in the manifold, no sweat. WHEW!!!!!!!!!!!! Barry
Barry You're not the first... won't be the last... Has the wife noticed her finches are lacking in the grooming department these days?
