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Beyond the Sea
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Discussion Starter · #1 ·
Can I use quadra jet primary jets in an old 1958 2 barrel Rochester carb (2GC I believe)? Or are they so different that they would not fit? I havent opened up the 2 barrel yet, but I just tested it today with an LM1 wide band O2 system and its too rich at idle and under full power.
I know q jets but havent tried to tune an ol' 2 barrel yet...
 

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If it`s too rich at idle adjust the idle mixture screws, clockwise leans the mixture. It`s been so long since I been in a 2 barrel if memory serves they don`t use the same rods but don`t quote me on that.
 

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WFO
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The jets are different. If you opt to modify the carb to accept different jets, go to Holley jets- they're more readily available.

Idle mixture can be controlled (should be able to, anyway) w/idle mixture screws. Changing the main jets will do little to nothing in this regard.

As for full power enrichment, this is also controlled by the power piston. It's vacuum modulated, so any loss of vacuum will be seen by the PP as a demand on the engine and cause it to open, allowing more fuel into the main metering system.

Be aware that restricted air bleeds on the high speed side will cause an over-rich condition. This can be due to a mechanical restriction (bent or crushed bleed) or just dirty.
 

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Beyond the Sea
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170 Posts
Discussion Starter · #4 ·
Here's a little more detail: the idle mixture is fine and steady at 13:1. But cruising around it is still at about 13:1 where (I judge by my Qjet experience) it should be around 15:1 or so. Under full throttle acceleration mixture gets overly rich at about 11:1 - 11.5:1. So I think one size or 2 sizes smaller jets plus retuning the idle circuit should help both power and gas mileage (the 58 Pontiac is too thirsty for a 283). A friend driving behind saw black smoke under acceleration as well.
 

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WFO
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Berliner Bel Air said:
Here's a little more detail: the idle mixture is fine and steady at 13:1. But cruising around it is still at about 13:1 where (I judge by my Qjet experience) it should be around 15:1 or so. Under full throttle acceleration mixture gets overly rich at about 11:1 - 11.5:1. So I think one size or 2 sizes smaller jets plus retuning the idle circuit should help both power and gas mileage (the 58 Pontiac is too thirsty for a 283). A friend driving behind saw black smoke under acceleration as well.
You can try going to a 1/16" lower float level. But ultimately, smaller jets may be needed.

Do you have a SBC in it? A '58 Pontiac should have a 370. '55's had the 287, '56 the 316, '57 the 347. Then in '59 the 389's came out, the rest, as they say, is history!

BTW, one of my short list of all-time favorite cars is a '58 Chieftain 4-speed w/Tri-Power. Black on black, black leather. A beautiful car, IMO. A guy down the street from our 'yard had one, he was always blowing head gaskets on it. But still an immaculate ride. Just beautiful, it was.
 

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A 2gc has an extra power enrichment tube it can be removed so that all full power fuel comes thru the jets and power piston.It just comes straight down from the top of the carb no other parts attached.GM used this for extra enrichment back when gas was a quarter.We removed them on circle track 2bbls so we could have complete control of fuel flow.
 
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