Quadrajet jetting advice needed
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Joined: Jan 2000
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From: Combaillaux
Quadrajet jetting advice needed
I changed my carburator from Holley to a very clean Quadrajet on my 327CI .
This one is from a 1972 350CI truck (704 2210 ) with original74 main jet and 43 main rod.
It's much too rich.
So I'm looking for an advice about a combo main jet / main rod to start from.
My engine is a 327CI with flat top pistons, Edelbrock Performer RPM 70cc heads and Crane Cam H-260-2 Intake @Cam 2847 @Valve 484 Exhaust @ Cam 3027 @Valve 515
This one is from a 1972 350CI truck (704 2210 ) with original74 main jet and 43 main rod.
It's much too rich.
So I'm looking for an advice about a combo main jet / main rod to start from.
My engine is a 327CI with flat top pistons, Edelbrock Performer RPM 70cc heads and Crane Cam H-260-2 Intake @Cam 2847 @Valve 484 Exhaust @ Cam 3027 @Valve 515
Melting Slicks
Joined: Nov 2006
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From: Apple Valley, MN
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
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From: New Braunfels Texas
I changed my carburator from Holley to a very clean Quadrajet on my 327CI .
This one is from a 1972 350CI truck (704 2210 ) with original74 main jet and 43 main rod.
It's much too rich.
So I'm looking for an advice about a combo main jet / main rod to start from.
My engine is a 327CI with flat top pistons, Edelbrock Performer RPM 70cc heads and Crane Cam H-260-2 Intake @Cam 2847 @Valve 484 Exhaust @ Cam 3027 @Valve 515
This one is from a 1972 350CI truck (704 2210 ) with original74 main jet and 43 main rod.
It's much too rich.
So I'm looking for an advice about a combo main jet / main rod to start from.
My engine is a 327CI with flat top pistons, Edelbrock Performer RPM 70cc heads and Crane Cam H-260-2 Intake @Cam 2847 @Valve 484 Exhaust @ Cam 3027 @Valve 515
Funny, I have a pristine example of that exact Q-Jet on the shelf but have never put it on anything yet......
Jebby
Last edited by Jebbysan; Mar 7, 2024 at 07:44 AM.
Old Pro Solo Guy
Joined: Dec 2017
Posts: 8,095
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From: Marlton NJ
You change both the rods and the jets to re-curve these carbs.
The fat part of the rod restricts fuel for idle/cruise range, the tips are much smaller to add fuel for WOT.
Which part do you need to richen?
And finding the right # parts these days is your biggest challenge.
The fat part of the rod restricts fuel for idle/cruise range, the tips are much smaller to add fuel for WOT.
Which part do you need to richen?
And finding the right # parts these days is your biggest challenge.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
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From: At my Bar drinking and wrenching in Lafayette Colorado
You can't compare the jetting in a pre-'70 small main air bleed carb to the jetting on a post-70 large main air bleed carb. The comparison is completely irrelevant.
If a 1972 7042210 large-bleed carb is running too rich with 74 jets in it, you have problems far beyond the jet size. A large-bleed carb with 74 jets is a very lean running carb. You have other problems if the carb is actually running rich. The jet size is not your problem.
If a 1972 7042210 large-bleed carb is running too rich with 74 jets in it, you have problems far beyond the jet size. A large-bleed carb with 74 jets is a very lean running carb. You have other problems if the carb is actually running rich. The jet size is not your problem.
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Joined: Jan 2000
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From: Combaillaux
The carburetor was remanufactured by uremco in 2011 and has not been used since. Everything seems to be in good condition.
The sparkplugs are black.
So if it's a lean running carb, what else should I check? float level, upper gasket, anything else ?
The sparkplugs are black.
So if it's a lean running carb, what else should I check? float level, upper gasket, anything else ?
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From: Virginia
Did you email @lars already? Please post some photos!
Melting Slicks
Joined: Nov 2006
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From: Apple Valley, MN
The fact that it was “remanufactured” means many possibilities for your issues. I know you are in France but you might want to seriously consider sending the carb to Lars in the USA. He is, by far and away, the most knowledgeable person in the world regarding the Quadrajet. 100% you will get a perfectly operating carb.
Le Mans Master
Joined: Oct 2010
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From: melbourne florida
2023 C3 of the Year Finalist - Modified
Gasoline in your country may be formulated or refined differently not sure if that's the case but there are definitely possibilities beyond jet sizes.
Did the Holley run better?
Did the Holley run better?
Tech Contributor
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From: At my Bar drinking and wrenching in Lafayette Colorado
Lars
V8FastCars@msn.com
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From: Combaillaux
The holley was an universal 4160, 600cfm, squarbore so I changed also the manifold for a spreadbore with the quadrajet.
Because I didn't had used the car for a long time before the carb changement, I can't really tell about the differnce between both carburators. It's just seems pretty similar too me.
Lars, your last post is really encouraging... ;-) but I send you an email to learn more about "Commercially Rebuilt Carb Problems" .
Because I didn't had used the car for a long time before the carb changement, I can't really tell about the differnce between both carburators. It's just seems pretty similar too me.
Lars, your last post is really encouraging... ;-) but I send you an email to learn more about "Commercially Rebuilt Carb Problems" .
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From: Combaillaux
So with the help of Lars, his paper "Commercially Rebuilt Carb Problems" as well as his comments on the photos of the carburetor that I sent him, it turns out that the power piston's bottom pin had been removed,I'm lucky they don't brake it inside, and that idle air bypass was plugged.
I machined a new pin which I re-sleeved in place and removed the lead plugs.
So now idle is much better, sparkplugs are no more black and the idle mixture screw finally useful.
There are small hesitations at cruise around 2000RPM. I suppose it's a little bit lean.
Do I have to try a smaller rod first or a larger jet to correct that problem?
Idle tube and idle down have also been changed by remanufacturer,
idle tube : 0.029
idle down restriction : 0.047
I machined a new pin which I re-sleeved in place and removed the lead plugs.
So now idle is much better, sparkplugs are no more black and the idle mixture screw finally useful.
There are small hesitations at cruise around 2000RPM. I suppose it's a little bit lean.
Do I have to try a smaller rod first or a larger jet to correct that problem?
Idle tube and idle down have also been changed by remanufacturer,
idle tube : 0.029
idle down restriction : 0.047
