Frequently Asked Questions

Short answer: AV gas is not a good street choice. It won’t burn pistons by itself, but modern AV gas is mostly unleaded/low-lead and formulated for altitude, so it gives little of the old octane benefit — and you’d have to re-jet to suit it. Higher octane only makes more power if you raise compression/advance to take advantage of it; a properly tuned engine makes the most power on the lowest octane that won’t detonate.

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Short answer: The fuel-gauge “sock” (filter) is a simple slip fit — it slides over the end of the pickup tube and has a built-in ring at the open end. The old one’s retaining ring comes off easily, and installation is just slipping the new sock on.

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Short answer: Either buy reproduction 1967–69 fuel lines, or make your own. To make them: a mandrel tubing bender (~$60, Sears Automotive) plus steel fuel/brake line from a parts store (sold in 25′ rolls) lets you build a line that looks like the factory piece.

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Short answer: On a 1967, the fuel line runs along the inside of the right (passenger) subframe from the rear of the car, then crosses to the left side along the front-subframe crossmember. A line follows the crossmember under the engine, joins the “Camaro” line with a short rubber hose, and the usual hose runs to the fuel pump — held by the same clips as the right-front brake line.

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Short answer: The original 400 Firebird fuel sending unit is GM #6427857 (“Gauge, Fuel Tank Unit”) — for 1967–68 F/8 with A/C and 1967–68 F/8 “400,” per the 1969 parts book. The key difference from the replacement units sold today is the vapor-return tube.

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Short answer: 400 engines and all A/C birds used a two-line sending unit (3/8″ fuel + 1/4″ return). The only off-the-shelf replacement is the single-line (326/350) unit — but the dual-line is reproduced.

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Short answer: The original 1969 tank finish was silver (galvanized). The Eastwood Company sells a close-duplicate coating.

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Short answer: You can tell without dropping the tank. Look at the fuel lines at the front-right of the tank: two lines = the two-tube unit (one fuel, one vapor return); one line = the one-tube unit.

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Short answer: Correct finish is a natural galvanized-steel tank with bare-steel (or gloss black) straps — per the Camaro Restoration Guide (Firebird and Camaro share the tank and straps). Clear-coating is a fine way to keep it fresh.

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Short answer: The 1968 (350/auto) vented through a vented gas cap.

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Short answer: The small vent tube on the filler neck is not unique to 400s. It’s a roughly 6–8″ tube that loops in a “U” and connects to a fitting on the body just above the filler tube, and members report it on 350 2-bbl and OHC-6 cars too.

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Short answer: One approach members use on a 1968 350: add lead substitute and run 92-octane gas to restore the octane the engine was originally designed for. (This started as a fix for acceleration and knocking problems that appeared when forced to switch to unleaded in the mid-1980s.)

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Short answer: Use the lowest octane that doesn’t cause detonation (pinging) — not simply the lowest available. Run too low and you’ll eventually break something; run higher than needed and you only waste money and raise emissions (it won’t help performance). 92 octane or higher won’t hurt anything.

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Short answer: Compression ratio drives the octane requirement. Per Pontiac engineer John Sawruk, the pre-1971 (~10:1) engines were qualified on 100 research octane — he suggested ~94 pump octane plus a can of booster. The 1968 engines that actually required premium were the H.O., Sprint, and Ram Air.

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Short answer: No special tool needed. Clean the area around the unit, then use a small brass drift to tap the lock-ring tabs (there are 3 or 4) evenly around to the unlock position. Lift the sending unit out carefully — the filter element is usually fragile with age — and check/clean the o-ring under the flange before reinstalling.

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Short answer: A pedal that only opens the throttle halfway usually means bent inner carb linkage (from a too-strong return spring, or someone stomping the pedal into the old horsepower-limiting throttle stop) — or, as the original poster discovered, a cracked accelerator-pedal mounting bracket. Check the pedal bracket and the carb’s inner linkage.

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Short answer: To rule out timing as an overheating cause: disconnect and plug the vacuum advance (its only purpose is gas mileage), then set the initial timing to 8–14° BTDC and see if it cools.

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Short answer: Two ways to set timing — by the numbers with a timing light, or by ear. Either way, start with the vacuum advance disconnected and plugged.

See also: Timing Adjustment to Fix Overheating Problems for how a manifold-vs-ported vacuum source affects timing (and cooling).

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