Anyone happen to have a vaccum port diagram for a 73' 7042240 carb. Im running this on a recently rebuilt 400 T-37. Im pretty sure I have everything hooked up right.Just wanted to view a diagram to verify vaccum ports. Thanks
There is really no reason for a vacuum diagram unless you are running the pollution controls. Everything else is really very simple. There are 2 types of vacuum available on the Q-jet, ported vacuum (passenger side top) and manifold vacuum (driver's side top). The vacuum advance can get ported or manifold, your choice. The air cleaner, vacuum storage(for heater controls), transmission modulator line, and power brakes get manifold vacuum. Did I miss anything?
Depending on the carb, there may be multiple sources of "ported" vacuum; and not all of them "turn on" at the same throttle opening. If one ported vacuum nipple has vacuum before/earlier than another, the one with vacuum earliest would be suitable for the vacuum advance; the one that has the greatest delay for vacuum would be used for the EGR valve. Again, depending on the carb, there may be nipples for fuel bowl vents; nipples to supply filtered air for a "heated air" choke, or a vacuum source to purge the charcoal canister. The choke pulloff(s) will be supplied vacuum via dedicated manifold-vacuum nipples. PCV gets manifold vacuum via a large nipple (generally 3/8" hose, and generally but not always at the front of the carb) and should never be "tee-d" into the vacuum supply for other vacuum accessories particularly the power brake booster.
Something to consider here is the possibilities appearing in the early '70's. Different vehicles with the same engine might have five or six different configurations. This was due to the evolving emissions requirements being applied to different models, based on engine, transmission, rear end combinations, with or without A/C, EGR, and AIR. GM, also knowing what was coming, in many cases, would try different combinations to evaluate reliability and durability, and emissions effectiveness. The underhood decal, which typically disappears after some five or six years, is usually the only source of info regarding the applicable hardware and configuration. You are better off knowing which emissions controls can be safely defeated, and how the necessary ones were connected. While I do not recommend defeating ANY of these devices, tampering is to be expected, and working with what you have remaining may be the only solution. Defeating EGR, and vacuum advance controls was common, frequently resulting in improved driveability, however, defeating the heated air cleaner and heat risers, though common, resulted in driveability losses, stalling either hot or cold, and difficulty starting. I can help with these issues, but knowing what remains will help. Typically, vacuum advance was ported, (available off-idle), air cleaner supply vacuum is manifold sourced, (always present), and most others can be left off. Vacuum advance should be carefully evaluated regarding sources, being aware of the damage constant ignition pinging can cause. I can offer personal assistance on a one-to-one basis. Ray
Re: 72' 800cfm carb diagram Yep it's a '72 sorry about that,fourth digit is a 2. Double checked and everything appears to be in the right spot. Thanks for the replies.
