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Old 04-13-2021, 08:05 AM
JLBIII JLBIII is offline
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Default Stock carb jet size

My 68 Firebird has the original Quadrajet model 7028264. Where can I find what size the original jets and metering rods were? Thanks

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Old 04-13-2021, 09:14 AM
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Is the motor stock and with its stock traverse type Muffler?

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Old 04-13-2021, 10:27 AM
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A Rochester carb book probably has it. Kenth probably knows.
I couldn't find your car though, but the ones close to it were 71/72 Jet and 40/42 rods. Should be in the ballpark anyway for starting out if you don't have any at all?



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Old 04-13-2021, 10:34 AM
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Right now it has 73 main jets and 42 rods. Currently has LT headers going to individual mufflers, no H or X pipe

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Old 04-13-2021, 10:37 AM
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FIREBIRD ALL A/T 400/400HO Quadrajet 7028264 uses #73 jets, #42 primary rods, secondary rods #7034377 stamped BE. 1/2 turn on airvalve spring preload, power piston spring #7037305.

Main jetting is fine, but you may find the .032" idle tubes and .043" idle down channels too small for today fuels, and i recommend .036" idle tubes and .050" idle down channels to have a strong/steady idle in gear and a smooth transition to low speed driving.

Also, i would replace the BE sec rods with DA or CE sec rods for better WOT respons.

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Old 04-13-2021, 11:39 AM
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Thanks Keith. Right now she idles fine but has a slight "stumble" from about 1400rpm up to 1900rpm. Once she hits 2000rpm she just takes off. The point where she takes off is very consistent, no variation that i can see/feel.

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Old 04-13-2021, 12:23 PM
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Is the engine still 100 percent completely "stock" or has it been modified at some point, different cam, heads, compression ratio, aftermarket distributor, etc?......

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Old 04-13-2021, 01:29 PM
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Quote:
Originally Posted by Cliff R View Post
Is the engine still 100 percent completely "stock" or has it been modified at some point, different cam, heads, compression ratio, aftermarket distributor, etc?......
Hi Cliff. According to PHS documents it's a number matching stock 400HO engine that has been fitted with LT headers and Davis HEI. I'm planning on putting the RARE exhaust manifolds on along with '68 style exhaust system

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Old 04-13-2021, 08:33 PM
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It will be fine if left alone but on this new fuel I like to add about 5 percent more across the board. Kenth mentions opening up the idle tubes and DCR's slightly and often that is enough as that move adds some fuel to the main system at light throttle via the transfer slots and mixture screw holes.

That carb also uses an upper idle airbleed adjustment behind the front vent. They are often backed out a bit. Turning them clockwise will also richen things up at idle/off idle and light cruise as well and many times that's enough without really changing any parts or opening up any holes anyplace.......

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73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
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Old 04-13-2021, 08:43 PM
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Swap meet. Get your year Q jet manual.

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Old 04-13-2021, 10:09 PM
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Quote:
Originally Posted by Cliff R View Post
That carb also uses an upper idle airbleed adjustment behind the front vent. They are often backed out a bit. Turning them clockwise will also richen things up at idle/off idle and light cruise as well and many times that's enough without really changing any parts or opening up any holes anyplace.......
Found what you're referring to on pg. 27 of your book. I'll check it tomorrow. Thanks Cliff

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Old 04-14-2021, 12:59 PM
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The air bleed adjustment screw was all the way down and bottomed out. Wish it would have been that simple.

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