Frequently Asked Questions
Find answers to Frequently Asked Questions for First Generation Firebirds that have been asked and answered on FGF. Special thanks needs to be given to all the FGF members who took the time to respond to other member's questions.
Engine - Carburetor
Short answer: The “best” build depends on your goals (match all the components to them), but for a normal streetable 350 the short version is:
- Intake: a 1967–72 4-bbl intake
- Carb: Quadrajet
- Cam: around .450″ lift; consensus is no more than 214/224 duration at .050″
- Heads: if virgin, you can mill up to .060″ (removes about 12 cc from the chambers)
A good order of operations: set general goals, then tune what you have (cheap gains), then address gearing, tires, and transmission/converter, and then the engine. For the full discussion, read Jim Hand’s articles and search the Q&A archives at classicalpontiac.com.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: The idle mixture screws are the only control for idle fuel mixture — the main jets meter everything above idle, and changing jets won’t affect the idle. Adjust the screws for the smoothest idle, then lean slightly.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: Converting a 1968 2-bbl to an Edelbrock Performer 4-bbl is straightforward; the fiddly parts are the throttle linkage/cable, the fuel line, and the vacuum connections.
- Throttle linkage: the stock cable won’t reach — use an aftermarket bracket (Edelbrock lists linkage accessories) to bring the cable closer, and fabricate a kickdown-switch mount from your 2-bbl parts if needed.
- Fuel line: Edelbrock fuel-line kit #8135 (hose, fittings, filter, clamps), plus a banjo fitting #8089 for low-profile air-cleaner clearance. No hard-line kits — make your own if you want hard line. Route rubber line away from heat.
- Vacuum: if the manifold has no vacuum fitting, the carb has three ports — the large center port at the base is PCV (keep it connected), a smaller full-time (manifold) vacuum port, and a ported (part-time) port. Most distributors use ported, but verify which yours needs, and cap any unused port.
- Valve-cover breather tube: either cap the valve-cover opening with a breather, or knock out the plug in the aftermarket air cleaner and route the hose there (a stock 4-bbl cleaner uses the hose as original).
- Air cleaner: any 4-bbl cleaner fits if the neck matches — pick one with the inlet on the correct side and not too tall (close the hood slowly to check).
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Content last modified: June 13, 2026 at 10:06 am
Short answer: Carburetor number 7037262 decodes as a 1967 (4th digit “7”), late-half-of-year (3rd digit “3”) unit for a California-emissions V-8 automatic (last digit even = automatic; odd would be manual). It doesn’t list as a Firebird carb — likely a GTO unit. It’s a rare carb worth trading, but not worth spending a lot to fix if it isn’t correct for your car.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: The two screws at the front base are the idle mixture screws — out (counter-clockwise) = richer, in = leaner. They only affect idle, not cruise mixture.
Setting them (ideal is an exhaust-gas analyzer, but by ear): with a warm engine, gently seat each screw counting the turns, then back both out to the smaller count. Adjust both 1/2 turn at a time — if it runs rougher you’ve gone too lean, so go back out; keep going for the smoothest idle, then lean it very slightly (back in ~1/2 turn).
Choke: it should just close after a long cool-off in mild weather (more tension in real cold), and be fully open after about 5 minutes of running (no more than 10).
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Content last modified: June 13, 2026 at 10:06 am
Short answer: Swapping a 1968 350 from 2-bbl to a Quadrajet 4-bbl isn’t difficult, but watch a few things: the intake casting, the throttle cable/bracket, and the air cleaner.
- Intake: spreadbore (Q-jet) castings are basically the same 1968–72. Avoid 1973+ (EGR) and 1976+ (restrictive ports, identified by a waffle imprint behind the carb flange). Some pre-1968 4-bbl intakes were squarebore (Carter AFB), and the 1967 Q-jet intake has an odd heat passage on the carb flange.
- Throttle cable/bracket: the 2-bbl cable won’t give full throttle travel. Reproduction 4-bbl cables are available from Performance Years; you’ll need to find or modify the bracket. (Pontiac used a rod in 1967, a cable for 1968+, and the design changed again around 1970–71 toward the Chevy style — so match the year.)
- Air cleaner: you’ll need a 4-bbl air cleaner (FGF, eBay, or Classical Pontiac classifieds for a stock-look one).
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Content last modified: June 13, 2026 at 10:06 am
Short answer: The chrome louvered “pancake” air cleaner was stock on 1967 Firebird 400s without A.I.R. (it was also used on Corvettes). California 400s, which came with the A.I.R. emissions system, used a traditional closed-snorkel air cleaner with a chrome top instead. Either way the car also had chrome valve covers, breather, and master-cylinder cover.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: On 1968 Quadrajets the Julian date code can be near the model number on the body, on the base at the rear, or (on some early-1968 carbs) missing entirely — e.g., the RA I 7028277 is often found with no date code. Early-1968 carbs are the most likely to lack it or have it on the base.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: Here’s how that set of engine/carb/manifold markings decodes:
- YR — engine usage/type code
- 33202 — Engine Unit Number
- 23N108627 — partial VIN, unique to the car the engine came from
- E220 (on the intake) — a date code (e.g., May 22, 1970?)
- 9796155 (on the exhaust manifold) — a part/casting number
- 17054905 — Rochester carburetor usage code
- 2738 — carburetor build-date code (e.g., 273rd day of 1968?)
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Content last modified: June 13, 2026 at 10:06 am
Short answer: The Distributor Vacuum Advance Valve Assembly (#9773623) was used on all 1968/69 Pontiacs with manual transmission and on 1967 manual-trans A.I.R. engines. It mounts on the right-rear of the intake manifold, and its plastic end cover is black (green, #9794257, on RA II engines). Don’t confuse it with the distributor vacuum control that attaches to the distributor itself.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: 1968 was the only year for a dual-diaphragm (advance/retard) distributor, which retarded timing under certain conditions for emissions. Owners complained of a slight backfire while coasting downhill or decelerating, and a service bulletin had dealers disconnect the retard side. Yours likely already has it disconnected — check for a separate vacuum nipple on the advance/retard unit and make sure that vacuum source is plugged.
[pdfjs-viewer url=/dtb/docs/68-T-2.pdf viewer_height=800px fullscreen=true download=false print=true]
[pdfjs-viewer url=/dtb/docs/68-T-2A.pdf viewer_height=800px fullscreen=true download=false print=true]
[pdfjs-viewer url=/dtb/docs/68-I-45.pdf viewer_height=800px fullscreen=true download=false print=true]
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Content last modified: June 13, 2026 at 10:06 am
Short answer: The 1968 dual-port unit is actually a combined advance/retard device for early emissions (paired with the redesigned 1968 heads). It isn’t strictly necessary — owners complained of popping in the exhaust from the retard function, and dealers frequently just disconnected the retard side.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: Yes — the 1967 Turbo 400 uses an electric kickdown (detent/passing-gear) switch, activated near full throttle. On a 1967 it’s a plunger switch mounted to the intake manifold near the left-rear of the carb (bracket held by the left-rear carb bolt), tripped by an extension bracket on the pedal linkage. Two wires: black, and black-with-green-stripe.
How it works (per Jim Hand): the vacuum modulator controls shift points only when there’s vacuum — at wide-open throttle there’s little/no vacuum, so the modulator can’t control WOT shifts. The detent (kickdown) system takes over at WOT: it forces the kickdown (3-2, 3-1, or 2-1), overrides the modulator, and raises clutch oil pressure for durability. So if the switch is misadjusted to trip at part throttle, the trans behaves as if you’re at WOT whenever it’s active; and running without a working detent causes accelerated clutch wear and lower WOT shift rpm. Adjust the switch toward the full-throttle end of the pedal travel. (See also the Engine FAQ — Carburetor for more.)
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Content last modified: June 13, 2026 at 10:06 am
Short answer: There’s a long-standing claim that 1967–68 Firebird 400 carbs had a small bent tab/link limiting how far the secondaries open — supposedly to keep the Firebird below the GTO’s rated horsepower under GM’s “10 lbs per hp” rule. Many magazines and books mention it, but it’s not fully settled.
The evidence both ways:
- Sources citing the tab include Hot Rod (3/68), Special Interest Autos (10/86), Motor Trend (12/91, Jim Wangers), The Fabulous Firebird (Lamm, 1979), and the Firebird Decoding Guide (DeMauro, 1997) — describing a tab on the throttle linkage limiting the secondaries to roughly two-thirds to 90% open.
- Against: Firebird and GTO carbs often share the same part number (so the same base plate and throttle linkage), with the real difference being the jetting. Careful inspection of original carbs hasn’t reliably turned up the tab — though one member reports an unrestored Firebird carb that has the bent tab and a different link part number.
Bottom line: the rated-horsepower difference between Firebird and GTO 400s is documented, but the exact carb component remains debated — research continues.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: The correct 1968/69 Firebird throttle cables by application are below — watch out for NOS cables being sold as something they’re not.
| Part # | Application | Tag | Length (overall / case) |
|---|---|---|---|
| 9792222 | 1968/69 F-6 1-bbl, F-8 2-bbl | Yellow | 19.5″ / 13.5″ |
| 9792223 | 1968/69 F-6 4-bbl | Blue | — |
| 9792224 | 1968/69 F-8 4-bbl | White | 18.0″ / 12.5″ |
The 9792222 (yellow tag) was apparently still available from GM for around $25.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: There’s a thin metal gasket (a sheet-metal plate with four holes) that goes between the Quadrajet base and the intake, covering a heat passage in front of where the carb sits. Missing it causes leaks and a miss. It’s about $5 at a speed shop, and it’s needed on both 1967 and 1968 Q-jet intakes.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: A common kickdown switch is the B&M unit (Summit part #BMM-20297). It’s intended to use an existing TH350 bracket when you swap in a TH400 — if you have a TH400 and no bracket, you’ll fabricate a small mounting bracket and a piece to attach it to the throttle. The linkage is adjustable and forgiving of mounting differences.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: 1967 Firebird 400s used one of five Rochester Quadrajet carburetors:
| Carb # | Application |
|---|---|
| 7027272 | 400, automatic |
| 7027273 | 400, manual |
| 7037272 | 400, automatic, w/ A.I.R. |
| 7037273 | 400, manual, Ram Air* |
| 7037276 | 400, automatic, Ram Air* |
* With or without A.I.R.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: High idle with the idle screw backed all the way out usually points to the secondaries not fully closing (commonly overlooked) or the throttle linkage/cable/bracket holding the throttle slightly open.
Things to check:
- Secondaries closed at idle; the set screw that adjusts the butterflies.
- Throttle cable orientation — with the linkage relaxed closed, the cable eye should reach the linkage without holding it open; reposition the bracket/cable if not.
- A bent accelerator pedal holding the throttle (rebend to spec).
- Choke fast-idle step binding (a shot of WD-40/Liquid Wrench frees it).
- Float needle not seating, an idle-stop solenoid stuck, ignition timing, and vacuum leaks.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: The 7028269 Rochester 4-bbl was used on all 1968 Tempest and Firebird 350, manual-trans, 4-bbl engines. It’s not rare — about 6,442 engines used it (3,784 “WK” Firebird 350 HO + 2,658 “WR” Tempest, manual), plus service-replacement carbs — so don’t get carried away bidding; ~$200 is plenty (a good rebuild can run $300+).
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Content last modified: June 13, 2026 at 10:06 am
Short answer: For 1967 Firebirds, only the 326 H.O. used the Carter carburetor — all other applications (including the 400) used the Rochester.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: The thermostatic vacuum switch (TVS, GM #3016754) sits at the front of the intake in the coolant passage and is a safety device against overheating. Normally it feeds ported vacuum to the distributor advance; when coolant rises above ~230°F it switches the advance to full manifold vacuum, advancing timing about 20° at idle to help the engine cool, then returns to ported vacuum once cooled. It was used on all 1968 V8s and 1969 V8 automatics (plus some early-1969 Ram Air III manuals and the 1971 455 HO).
- 1968 cars use a 5-hose vacuum harness (the two extra hoses are the idle-speed retard — the dual-port advance retards idle timing 10° for emissions); 1969 V8s and the ’71 455 HO use the 3-hose type.
- Hose color codes (supply lines to the TVS): red-striped = manifold vacuum; ported vacuum runs through a small steel pipe forward of the carb; the yellow hose (1968 only) is the idle-retard supply.
- Service Bulletins 68-T-2 (10/16/67) and 68-T-2A (1/4/68) addressed poor idle / harsh 2-1 downshift on 1968 2-barrel automatics (and full-size 4-barrel automatics): remove the two idle-retard hoses, loop the two switch holes with a shortened hose to keep dirt out, and readjust idle.
5-port switch hookup:
________ / | (1) | | (4) | | | | (2) | | | | (5) | | / | (3) / \_________ /
- To the vacuum port on the front of the carb (steel routed line)
- To the “Tee” at the rear of the carb
- To the distributor advance
- (4 and 5) looped together at the switch
From the 1968 Diagnostic Manual:
Fig 6D-9 — Components of the Controlled Combustion System
[pdfjs-viewer url=/files/FAQ/docs/6D-9.pdf viewer_height=800px fullscreen=true download=false print=true]
Fig 6D-10 — Distributor Vacuum Layout, V-8 2-Bbl.
[pdfjs-viewer url=/files/FAQ/docs/6D-10.pdf viewer_height=800px fullscreen=true download=false print=true]
Fig 6D-11 — Distributor Vacuum Layout, V-8 4-Bbl.
[pdfjs-viewer url=/files/FAQ/docs/6D-11.pdf viewer_height=800px fullscreen=true download=false print=true]
Fig 6D-12 — Vacuum Routing Chart
[pdfjs-viewer url=/files/FAQ/docs/6D-12.pdf viewer_height=800px fullscreen=true download=false print=true]
Fig 6D-13 — Vacuum Routing Chart
[pdfjs-viewer url=/files/FAQ/docs/6D-13.pdf viewer_height=800px fullscreen=true download=false print=true]
Fig 6D-14 — Vacuum Routing Chart
[pdfjs-viewer url=/files/FAQ/docs/6D-14.pdf viewer_height=800px fullscreen=true download=false print=true]
A list member’s compiled research comparing the available documents:
[pdfjs-viewer url=/files/FAQ/docs/TVS/68VacuumDialog.pdf viewer_height=800px fullscreen=true download=false print=true]
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Content last modified: June 13, 2026 at 10:06 am
Short answer: The TH350 kickdown cable snaps into a square hole on the carburetor side of the throttle bracket. You need the correct 4-bbl bracket with that square hole — a 2-bbl bracket leaves the cable about 3/4″ short, and the ~$80 reproduction brackets are for 1968 and don’t have the TH350 square hole. (If you find a 4-bbl cable-mount bracket with the TH350 hole, grab it.)
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Content last modified: June 13, 2026 at 10:06 am
Short answer: An “F2”-stamped bracket is for a 2-bbl. The correct 1969 Firebird 4-bbl throttle-cable bracket is 9797415, stamped “F4.” There’s no difference between automatic and manual.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: With an Edelbrock Performer intake and 600 carb on a 1968, the stock bracket is too short. Edelbrock’s #8015 “Pontiac” bracket is really just instructions to drill/bend your original bracket — awkward, and it assumes you have the original (which runs ~$75 at Ames).
A cleaner solution: a Lokar 24″ braided throttle cable plus a Lokar throttle-cable bracket (sold separately) — stainless, with dual return springs; it installs easily and looks good. Available at Summit Racing.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: The GM part number for the kickdown switch (1968 400/TH400, “M-40”) is #9785545 — the same part used on 1965–66 full-size and 1967–69 Firebird M-40 applications.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: For a 1968 with the dual vacuum-advance setup, there’s a thermostatic control switch on the passenger side of the intake with five ports:
- DA — distributor advance
- DR — distributor retard
- CA — carb advance (likely the ported vacuum source)
- CR — carb retard
- Manifold vacuum (from the bottom rear of the carb)
On automatics, the vacuum modulator also connects to manifold vacuum. AMES sells the control switch (~$35) and color-correct vacuum hose kits (~$54) with a diagram.
See also the “Vacuum Hose Diagrams for 1968” FAQ for the actual diagrams.
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Content last modified: June 13, 2026 at 10:06 am
Short answer: The correct 1968 400 vacuum-routing diagrams are below. (A common overheating cause is the distributor vacuum advance hooked to manifold vacuum instead of ported — and previous owners often cap off ports that should be connected.)
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