Quadrajet

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Oct 23, 2013 | 09:46 AM

DM76

Thread Starter

Intermediate

Joined: Jan 2010

Posts: 26

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From: Balto Md

Quadrajet

OK, I have rebuilt my carb again and still runs rich. It is a 76 vette carb # 17056206. It has 76 jets in it and I'm thinking its to much. And now it looks like the power piston is stuck. I know I need to take it apart and replace the plastic retainer but does anyone know the right jet size before I take it back apart? And if I change the jets to smaller ones should I change the 44 26 tip metering rods?

Oct 23, 2013 | 10:24 AM

MelWff

Race Director

Joined: May 2006

Posts: 18,604

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77 is the correct number download this document and scroll down

http://www.corvettefaq.com/c3/QJetTuningPaper.doc

Oct 23, 2013 | 01:10 PM

lars

Tech Contributor

Joined: Aug 1999

Posts: 14,356

Likes: 6,328

From: At my Bar drinking and wrenching in Lafayette Colorado

If you're running rich, you have problems not related to the jets. You need the 77 jets in that carb for it to run right. The rods should be 48's (48K). There is no need to replace the plastic power piston retainer - it has no effect on performance or operation, unless it is broken in a way which jams the power piston.

Lars

Last edited by lars; Oct 23, 2013 at 01:13 PM.

Oct 23, 2013 | 10:16 PM

73, Dark Blue 454

Melting Slicks

Joined: Mar 2005

Posts: 2,838

Likes: 10

From: Austin TX

How do you know she's rich? If she smells rich at idle, your float could be maladjusted.

Oct 24, 2013 | 12:21 PM

Eljay

Burning Brakes

Joined: Jun 2013

Posts: 1,076

Likes: 148

From: Hunterdon Cty NJ

Lars, I gave the paper a quick read and that is some great stuff! I have been thinking that I would really like to know about tuning Q-jets and tihis will be the ticket, thanks for taking the time to put this together.

Oct 24, 2013 | 01:18 PM

lars

Tech Contributor

Joined: Aug 1999

Posts: 14,356

Likes: 6,328

From: At my Bar drinking and wrenching in Lafayette Colorado

I don't show that I have sent you a paper... Don't use any of my papers you find posted on the Internet, including the ones posted here on this Forum: Those papers are outdated and obsolete - don't use them. For current, valid papers, e-mail me directly a request for the papers you want.

Lars
V8fastCars@msn.com

Oct 24, 2013 | 07:31 PM

DM76

Thread Starter

Intermediate

Joined: Jan 2010

Posts: 26

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From: Balto Md

Thanks I appreciate the help. Found a carb shop close by and they said the same thing. The 77 jets and 48k rods are right. But I have 76 jets in carb. Took the air horn back off and one of the metering rod arms was bent down. Bent it back in place and polished the power valve assembly to a mirror finish, recommended by shop to prevent sticking. Put everything back together and when for test ride. What a deference. I also tapped the air horn so I can adjust the auxiliary for power valve. Can't final tune car yet until MSD distributor comes in hopefully tomorrow. Old one just plain worn out. Thanks again.

Oct 24, 2013 | 09:55 PM

gcusmano74

Drifting

Joined: Mar 2011

Posts: 1,886

Likes: 9

Yes. When the factory stuff is set up correctly, these cars will run and drive well. You don't have to drop a dumptruck load of cash into them .
You can spend a bunch of money on trick parts, and make the car DIFFERENT. But it's not so easy to make the car BETTER.

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Oct 25, 2013 | 10:21 AM

lars

Tech Contributor

Joined: Aug 1999

Posts: 14,356

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From: At my Bar drinking and wrenching in Lafayette Colorado

Quote:

Originally Posted by DM76

Found a carb shop close by and they said the same thing. The 77 jets and 48k rods are right. But I have 76 jets in carb.

I wouldn't worry about a 1-size jet discrepancy. Your 44K rods are going to run you a little rich at cruise, but you can offset that by running the APT setting a little deeper. If I were rebuilding the carb for you, I'd put the "correct" parts in it, but for all practical purposes, your carb is going to run fine as jetted, providing you have all other parameters setup up correctly.

Lars

Oct 25, 2013 | 09:12 PM

#10

DM76

Thread Starter

Intermediate

Joined: Jan 2010

Posts: 26

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From: Balto Md

I did run the APT deeper. I'm at 2 turns from bottom now. Put in MSD distributer tonight and hope to start it up and finish tuning tomorrow. I'm keeping my fingers crossed. I was getting to much advance at idle before.

Oct 27, 2013 | 09:04 AM

#11

Eljay

Burning Brakes

Joined: Jun 2013

Posts: 1,076

Likes: 148

From: Hunterdon Cty NJ

Hey Lars, I was looking at the link that Melwff posted, if that is not correct info I will email you for the correct info. I see you also have timing info. I want my 70 454 to run correctly. Thanks

Oct 27, 2013 | 09:59 AM

#12

scottyp99

Le Mans Master

Joined: Mar 2008

Posts: 5,948

Likes: 72

From: Oxford MA-----You just lost the game!!!!

Quote:

Originally Posted by DM76

Could you go into a little more detail about "getting to much advance at idle"? How much advance were you getting? It's kind of unusual to see a distributor that is "worn out", they only spin at half the engine speed.

Scott

Oct 27, 2013 | 11:05 AM

#13

lars

Tech Contributor

Joined: Aug 1999

Posts: 14,356

Likes: 6,328

From: At my Bar drinking and wrenching in Lafayette Colorado

Quote:

Originally Posted by Eljay

Hey Lars, I was looking at the link that Melwff posted, if that is not correct info I will email you for the correct info. I see you also have timing info. I want my 70 454 to run correctly. Thanks

None of the sites posting my papers keep the papers up to date, resulting in obsolete and outdated info being posted. Don't use any of my papers posted by others on the 'Net. Current, valid papers are available by e-mailing me a request for the papers. You can also obtain a complete listing of all tech papers I have available by dropping me an email request.

Lars
V8FastCars@msn.com

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